Thermoelectric Properties of Fe0.2Co3.8Sb12-xTex ... - Physics

FOREWORD
As a periodic review of its activities, the Department of Physics has
been organizing In-house Symposium on annual basis during recent years.
This one-day symposium usually consists of oral presentations by faculty
members, post-docs and students, and poster presentations by all those who
would like to present their recent results. This year we have a total of 21
talks and 41 posters. I hope this package would be a reasonable
representation of the ongoing research activities in the department. This
event is also particularly useful to freshers to familiarize themselves with the
current research activity in our Department in various branches of Physics.
I would like to thank Arindam Ghosh, Prateek Sharma and Vijay
Shenoy of our department, and PDA, who have shouldered the responsibility
to organize this In-house Symposium. I urge all of you to actively participate
in this important scientific activity. I hope you will all have an enjoyable and
fruitful day.
Prof. H. R. Krishnamurthy
Chairman
November 23, 2012

Department of Physics, IISc Bangalore
Inhouse Symposium 2012
November 23, 2012
Auditorium, New Physical Sciences Building
Programme
Session I 9:00-10:30 Chair: P. S. Anil Kumar
T01 9:00-9:15 Tarun Deep Saini
Spiral patterns and instabilities in astrophysical disks
T02 9:15-9:30 Subhamoy Ghatak
Possible nature of internal disorder in ultra-thin MoS 2
FET
devices
T03 9:30-9:45
Rupamanjari Majumder
T04 9:45-10:00 K. Sathya Narayanan
T05 10:00-10:15 Srijit Goswami
T06 10:15-10:30 Anbalagan Ramakrishnan
Wave Dynamics in a Mathematical Model for Human Cardiac
Tissue with Randomly Distributed Fibroblasts.
A new model of flow induced voltage generation in cabon
nanotubes based on van der Waals friction
Landau Level Spectroscopy of Broken Symmetry States in
High Mobility Graphene on Boron Nitride
Thermoelectric Properties of Fe 0.2
Co 3.8
Sb 12-x
Te x
Skutterudites
10:30-11:00 Tea

Session II 11:00-1:00
T07 11:00-11:15
Chair: Aveek Bid
Jaydeep K. Basu
Signature of novel plasmonic Dicke effect in 2D quantum dot
solids mediated by surface plasmons of embedded
nanoparticles
T08 11:15-11:30
Sivasurender Chandran
Evidence of gradient in dynamics of confined polymers
T09 11:30-11:45
Ananyo Maitra
Nuclear spin
T10 11:45-12:00
Vikram Rathee
A reversible shear-induced crystallization above equilibrium
freezing temperature in mixed surfactant system
T11 12:00-12:15
Kaustuv Manna
T12 12:15-12:30 D. Venkateswarlu
T13 12:30-12:45 Sujit Kumar Nath
In Search for the Origin of Glassiness in La 0.85
Sr 0.15
CoO 3
Confinement of Spin Waves in Grids of Permalloy Nanowires
Magnetohydrodynamic stability of stochastically driven
accretion flows
T14 12:45-1:00
Vijay B. Shenoy
1:00-2:00 Lunch
Session III 2:00-4:30 Poster Session
Flow enhanced pairing and other stories of fermions in
synthetic gauge fields
4:30-5:00 High Tea

Session IV 5:00-7:00
T15 5:00-5:15
Chair: Ramesh Mallik
K. Ramesh
A unique electrical switching behaviour in Cu-As-Se
glasses
T16 5:15-5:30
Y. Jayasubba Reddy
T17 5:30-5:45 Nitin Kumar
T18 5:45-6:00 R. Koushik
T19 6:00-6:15 Indrani Banerjee
T20 6:15-6:30 Chanchal Sow
T21 6:30-6:45 Suropriya Saha
Heteronuclear Double Quantum Correlation Experiments
Involving Protons for the study of Partially Ordered and Rigid
Systems
Self-propelled granular rod amid a noisy medium: An
experimental test of Isometric Fluctuation-Relation
Probing superconductivity in the 2D limit using resistivity
noise
Nucleosynthesis inside gamma-ray burst accretion disks and
associated outflows
Freezing of the octahedral tilt near ferromagnetic transition
and appearance of a glassy phase at low temperature driven by
the tilt instabilities in SrRuO 3
Single-particle and collective behaviour of colloidal swimmers
6:45-7:00 Concluding Remarks, Best Poster Award
7:00-7:30 Vishwamitra Memorial Prize
7:30-8:30 Dinner

List of Posters
No. Presenter Title
P01
Arnab Roy
Study of switching field statistics of Permalloy (Ni80Fe20 ) Hall bars
by planar Hall effect
P02 Sudeesh K.
Unzipping Force Analysis to determine binding specificity of RNA
Polymerase to T7A1 promoter sequence
P03 Bidya Binay Karak Why does sun occasionally stop giving sunspots for several years?
P04
P05
Jayantha P. Vyasanakere
Anbalagan Ramakrishnan
Can interaction between emergent excitations be independent of the
constituent interactions?
Thermoelectric Properties of Fe 0.2
Co 3.8
Sb 12-x
Te x
Skutterudites
P06 Paritosh Karnatak High mobility graphene devices
P07
R.V. Sudheer Kumar
Measurement of Proton-Carbon Dipolar Couplings using an improved
DAPT pulse sequence
P08 Kowsalya Devi Pavulur Ultrafast NMR Techniques in Inhomogeneous Magnetic Fields
P09
P10
P11
P12
P13
P14
P15
M. Prashantha
Avradip Pradhan
V.S. Manu
Siddharth Madhav Khare
Semonti Bhattacharyya
Pradeep Kumar
Amit Kumar Majhi
Low temperature electrical transport studies on carbon nitride films
prepared by chemical vapour deposition
Investigating DNA hybridization through changes in conductance of
ultrathin Au nanowires
Quantum Simulation of Dzyaloshinsky-Moriya Interaction
Measurement of Forces applied by C. elegans moving on Agarose
surfaces.
Low frequency noise in Topological Insulator Bi 1.5
Sb 0.4
Te 1.7
Se 1.3
Superconducting fluctuations, Anomalous Phonons and Electronic
excitations in iron-based superconductors
Molecular dynamics simulation of electroporation of lipid bilayer
membrane
P16 Anindita Sahoo Transport properties and noise in hydrazine reduced graphene oxide.
P17 Rajan Modak Thermalization threshold in models of 1D fermions
P18
P19
P20
Debayan Dey
Shibu Saw
Gajanan V. Honnavar
Random matrix theory and gene correlation coefficient statistics of
DNA- Microarray data: Application in understanding the system
biology of gene regulation
Violation of Guggenheim Adsorption Rule at Wall-Liquid Interface in
Binary Lennard-Jones Mixture
Study of effect of alkali mixture on V - O bond length in Oxyfluoro
Vanadate glasses using Raman spectroscopy.

P21
Saquib Shamim
Suppression of localization in two dimensionally doped
semiconductors at half-filling
P22 Hariharan N.
Magnetic, Dielectric and Transport Studies of Single Crystal
Tb 0.5
Sr 0.5
MnO 3
P23
P24
P25
P26
Nairita Pal
Ch. Raju
Baban Wagh
Yogeshwar Prasad
Direct Numerical Simulation of Turbulence in the Two-Dimensional
Navier-Stokes-Cahn-Hilliard Equations
Thermoelectric properties of chalcogenide based Cu 2+x
ZnSn 1-x
Se 4
Thermal Conduction, Feedback and Multiphase Gas in Galaxy
Clusters
Realization of Fermionic Superfluid State in an Optical Lattice via a
Bilaryer Band Insulator
P27 Arpita Roy Superbubble breakout and galactic winds from disk galaxies
P28
Hemant Kumar
Flow Induced Alignment of water molecules conned inside carbon
nanotube: Insight from MD Simulations
P29 Mohammed Ali Aamir Large linear magnetoresistance in a GaAs/AlGaAs heterostructure
P30
P31
P32
P33
P34
P35
P36
Vidya Kochat
Amal Medhi
Sudeep Kumar Ghosh
Medini Padmanabhan
Mitali Banerjee
Achintya Bera
Sreetama Das
Universal Conductance Fluctuations as a direct probe to valley
coherence and universality class of disordered graphene
Sensory organ like response determines the magnetism of zigzagedged
honeycomb nanoribbons
Evolution of fermionic superfluid across the crossover from three to
two dimensions
Induced photoconductivity in large area graphene by electrochemical
deposition of thin films
Microwave assisted synthesis of single crystalline ternary alloy-Bi2-
xSbxTe3 for thermoelectric applications
Sharp Raman anomalies and broken adiabaticity at a pressure
induced transition from band to topological insulator in Sb2Se3
Using cis peptide containing fragments for functional annotation of
proteins
P37 Pramod K. Verma Study of Phonon anharmonic effects in pyrochlores
P38 Kallol Roy Optoelectronic properties of graphene-MoS2 hybrids
P39
P40
K.S. Vasu
Upasana Das
Bio– sensors based on electrical and optical properties of Carbon
nanotubes & Graphene oxide
Violation of Chandrasekhar mass limit: Strongly magnetized white
dwarfs as progenitors of super-Chandrasekhar type Ia supernovae
P41 Arijit Haldar Superfluidity in bricks!

TALK
ABSTRACTS

Spiral Patterns and Instabilities in Astrophysical Disks
Tarun Deep Saini
Department of Physics, IISc Bangalore

Possible nature of internal disorder in ultra-thin
MoS 2 FET devices
Subhamoy Ghatak, Paromita Kndu, N. Ravishankar and Arindam Ghosh
We investigate possible existence of intrinsic disorder in ultrathin MoS 2 thin film transistors.
For that we perform three kinds of independent electrical measurements on two classes of
MoS 2 -FET devices, on SiO 2 and on single crystalline hexagonal boron nitride (hBN)
substrate. Using time averaged transport measurement, we find that the device quality in
terms of mobility and charge relaxation remains almost similar for both the classes. We also
study low frequency 1/f noise, sensitive to charge dynamics of system and observe that in
both classes number density (n) fluctuation is the dominant mechanism of 1/f noise. From
this, we predict that although external source of disorder can’t be ruled out, internal disorder
might be the dominant source of disorder in atomically thin MoS 2 films.

Wave Dynamics in a Mathematical Model for Human Cardiac Tissue with
Randomly Distributed Fibroblasts.
Rupamanjari Majumder 1 , Alok Ranjan Nayak 1 , and Rahul Pandit 1,2 .
1
Centre for Condensed Matter Theory, Department of Physics, Indian Institute of Science, Bangalore, India
2
Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India
We present a comprehensive numerical study of spiral-and scroll-wave dynamics in a state-of-the-art mathematical
model for human ventricular tissue with fiber rotation, transmural heterogeneity, myocytes, and fibroblasts. Our
mathematical model introduces fibroblasts randomly, to mimic diffuse fibrosis, in the ten Tusscher-Noble-Noble-
Panfilov (TNNP) model for human ventricular tissue; the passive fibroblasts in our model do not exhibit an action
potential in the absence of coupling with myocytes; and we allow for a coupling between nearby myocytes and
fibroblasts. Our study of a single myocyte-fibroblast (MF) composite, with a single myocyte coupled to Nf fibroblasts
via a gap-junctional conductance Ggap , reveals five qualitatively different responses for this composite. Our
investigations of two-dimensional domains with a random distribution of fibroblasts in a myocyte background reveal
that, as the percentage Pf of fibroblasts increases, the conduction velocity of a plane wave decreases until there is
conduction failure. If we consider spiral-wave dynamics in such a medium we find, in two dimensions, a variety of
nonequilibrium states, temporally periodic, quasiperiodic, chaotic, and quiescent, and an intricate sequence of
transitions between them; we also study the analogous sequence of transitions for three-dimensional scroll waves in a
three-dimensional version of our mathematical model that includes both fiber rotation and transmural heterogeneity. We
thus elucidate random-fibrosis-induced nonequilibrium transitions, which lead to conduction block for spiral waves in
two dimensions and scroll waves in three dimensions. We explore possible experimental implications of our
mathematical and numerical studies for plane-, spiral-, and scroll-wave dynamics in cardiac tissue with fibrosis.
Based on:
Majumder R, Nayak AR, Pandit R (2012) Nonequilibrium Arrhythmic States and Transitions in a Mathematical Model
for Diffuse Fibrosis in Human Cardiac Tissue. PLoS ONE 7(10): e45040. doi:10.1371/journal.pone.0045040

A new model of flow induced voltage generation in
Carbon Nanotubes based on van der Waals friction
K. Sathya Narayanan and A.K. Sood
Department of Physics, Indian Institute of Science, Bangalore-560012, India.
We present here a simple model to explain the plethora of experimental results
concerning the flow induced voltage generation in carbon nanotubes which, thus
far, have been only inadequately explained. To do this, we consider the zeroth
order picture of the alignment of water molecules confined inside the nanotubes
subject to the force field exerted by the imposed flow outside the tubes. These
aligned water molecules polarize the nanotubes containing them, thereby
inducing a potential difference across its length. Importantly, we model this force
field as due to the van der Waals (VdW) frictional stress that exists between any
two dissipating dielectric media in relative motion with each other, which, here, is
between the confined water molecules and the flowing liquid. This simple model,
surprisingly, captures the qualitative behavior observed in the experiments such
as: induced voltage as a function of flow velocity, gate voltage and electrolyte
concentration. Further, this also explains the apparently unrelated non-local
voltage generation observed in isolated carbon nanotubes when filled with water
vapor. We extend this even more to try and understand the intriguing
phenomenon of flow induced voltage generation in carbon nanotubes trapped in
Ice, wherein the flowing medium is well isolated from the nanotubes by a
sufficiently thick layer of ice. We believe that this understanding is crucial to
optimization of future energy harvesting devices.

Landau Level Spectroscopy of Broken Symmetry States in High Mobility
Graphene on Boron Nitride
Srijit Goswami, Paritosh Karnatak and Arindam Ghosh
The presence of spin and valley degeneracy in graphene gives rise to four-fold degenerate
Landau levels (LLs) in the presence of a magnetic field perpendicular to the plane of the
graphene. Graphene devices on silicon oxide substrates typically exhibit very low mobility,
resulting in significant broadening of LLs. As a result, any broken symmetry states are
difficult to observe at reasonable magnetic fields.
Placing graphene on atomically flat hexagonal Boron Nitride (BN) results in significantly
higher carrier mobility. We have fabricated such high mobility graphene-BN
heterostructures and show that the four-fold degeneracy of the LLs is completely lifted at
moderate magnetic fields. Such broken symmetry states have been observed in a few
studies previously, however their exact nature is still a matter of debate.
We also show that charge transfer between graphene and a nearby defect site gives rise to
discrete jumps in the resistance. In the presence of a magnetic field the size and nature of
these resistance jumps is particularly sensitive to the position of the Fermi level. We discuss
some preliminary results which indicate that such a graphene-defect system may allow for a
more sensitive spectroscopy of the LLs, as compared to time averaged transport.

Landau Level Spectroscopy of Broken Symmetry States in High Mobility
Graphene on Boron Nitride
Srijit Goswami, Paritosh Karnatak and Arindam Ghosh
The presence of spin and valley degeneracy in graphene gives rise to four-fold degenerate
Landau levels (LLs) in the presence of a magnetic field perpendicular to the plane of the
graphene. Graphene devices on silicon oxide substrates typically exhibit very low mobility,
resulting in significant broadening of LLs. As a result, any broken symmetry states are
difficult to observe at reasonable magnetic fields.
Placing graphene on atomically flat hexagonal Boron Nitride (BN) results in significantly
higher carrier mobility. We have fabricated such high mobility graphene-BN
heterostructures and show that the four-fold degeneracy of the LLs is completely lifted at
moderate magnetic fields. Such broken symmetry states have been observed in a few
studies previously, however their exact nature is still a matter of debate.
We also show that charge transfer between graphene and a nearby defect site gives rise to
discrete jumps in the resistance. In the presence of a magnetic field the size and nature of
these resistance jumps is particularly sensitive to the position of the Fermi level. We discuss
some preliminary results which indicate that such a graphene-defect system may allow for a
more sensitive spectroscopy of the LLs, as compared to time averaged transport.

Signature of novel Plasmonic Dicke effect in 2D quantum dot solids
mediated by surface plasmons of embedded nanoparticles
Jaydeep Basu
Quantum dot ensembles and solids find numerous applications from solar cells to novel
nano-lasers. Understanding their optical and electrical properties and the ability to tune
them is thus of vital importance.
Here, we will discuss our recent work on photoluminescence (PL) from two dimensional
solids made of CdSe quantum dots lightly doped with metal nanoparticles. The emission
from the quantum dot solid can be tuned by controlling the packing of the solid, spectral
overlap between the quantum dots and the metal nanoparticles as well as through doping
concentration. While the PL from the quantum dots show expected variation at low
density and large doping of gold nanoparticles, unexpected strong enhancement in PL
occurs at low and intermediate doping, especially when the quantum dots and metal
nanoparticles are spectrally at resonance. A recently suggested model [3] of plasmon
mediated superradiance, due to virtual plasmon exchange between proximal quantum
dots, leading to such enhancements seems to be the likely cause of such an unusual
effect.
Acknowledgements: The work presented here has been done in collaboration with
Laxminaryanan Tripathi, M. Praveena, M. Haridas.
References:
1. L. N. Tripathi, M. Praveena, J. K. Basu, Plasmonics (2012).
2. M. Haridas, L. N. Tripathi and J. K. Basu, Applied. Physics. Letter, 98, 063305
(2011).
3. Vitaliy N. Pustovit and Tigran V. Shahbazyan, Phys Rev Lett. 102, 077401
(2009).

Evidence of gradient in dynamics of confined polymers
Sivasurender Chandran 1 , N. Begam 1 , J. K. Basu 1 and M. K. Mukhopadhyay 2
1 Department of Physics, Indian Institute of Science, Bangalore – 560012
2 Applied Materials Science Division, Saha Institute of Nuclear Physics, Kolkata – 700064
Particle segregation to surface/interface, surface mobility of the particles, interfacial
viscosity and thereby the gradient in the dynamics of polymer thin films is a matter of debate,
which generated lot of controversies over the last few years. We report [1] the evidence of
gradient in dynamics by probing the diffusion coefficient of polymer grafted nanoparticles
(PGNP) dispersed in polymer thin films of different thickness viz., 2.5R g and 8R g of the matrix
chains (R g is the radius of gyration). Using surface x-ray scattering, we observe a systematic
vertical dispersion of PGNP from a pinned in substrate interface layer to the surface on thermal
annealing. Even after annealing at high temperature (T>>T g ) and longer times, a fraction of
PGNP pertain to stay at the substrate forming a stable interface layer. This hints about the low
mobility of particles at the substrate interface and also emphasizes the presence of high
viscous/gel-like interfacial layer. Real space microscopic images show the formation of lateral
domains of the particles at air surface suggesting the higher surface mobility. In addition, it is
also observed that the fraction of particles in the air surface is more in annealed thinner films
compared to the thicker ones. Thus, we have correlated the observed lateral and vertical
dispersion and its evolution with annealing, to the gradient in dynamics along the thickness of
the thin films.
[1] Sivasurender Chandran, J. K. Basu and M. K. Mukhopadhyay, in communication

Nuclear spin
Abhishek Kumar
Mechanobiology Institute and Department of Biological Sciences, NUS, Singapore 117411 and
National Centre for Biological Sciences, TIFR, Bangalore 560065, India
Ananyo Maitra*
Department of Physics, Indian Institute of Science, Bangalore 560012 , India
Madhuresh Sumit and G.V. Shivashankar
Mechanobiology Institute and Department of Biological Sciences, NUS, Singapore 117411
Sriram Ramaswamy
Department of Physics, Indian Institute of Science, Bangalore 560012 , India and
TIFR Centre for Interdisciplinary Science, 21 Brundavan Colony,
Osman Sagar Road, Narsingi, Hyderabad 500 075, India
(Dated: November 15, 2012)
We study the nuclear dynamics of single fibroblast cells, with effects of cell-migration suppressed
by plating onto fibronectin-coated micro-fabricated patterns. It is observed that on circles, squares
and equilateral triangles, the nucleus undergoes persistent rotational motion, while on high-aspectratio
rectangles of the same area it moves only back and forth. We show that our observations
can be understood through a hydrodynamic approach in which the nucleus is treated as a highly
viscous inclusion residing in a less viscous fluid of orientable filaments endowed with active stresses.
Lowering actin contractility selectively by introducing blebbistatin at low concentrations drastically
reduced the speed and persistence time of the angular motion of the nucleus, lending credence to
our ideas. Time-lapse imaging of actin also revealed a correlated hydrodynamic flow around the
nucleus, with profile and magnitude consistent with the results of our theoretical approach. Coherent
intracellular flows and consequent nuclear rotation thus appear to be a generic property that cells
must balance by specific mechanisms in order to maintain nuclear homeostasis.
Keywords:

A reversible shear-induced crystallization above equilibrium
freezing temperature in mixed surfactant system
Vikram Rathee 1 , Rema Krishnaswamy 2 , Antara Pal 3 , V. A. Raghunathan 3 , Marianne Imp´eror 4 , Brigitte
Pansu 4 and A.K. Sood 1,2
1 Department of Physics, Indian Institute of Science, Bangalore 560012, India,
2 Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P.O., Bangalore 560064, India,
3 Raman Research Institute, Bangalore-560080, India, and
4 Laboratoire de Physique des Solides, UMR 8502 CNRS, Bat 510, Universite' Paris-Sud 11, 91405 Orsay
Cedex, France.
Shear driven crystallization is a well studied phenomenon in colloidal suspensions, polymer melts,
surfactant mesophases, molecular liquids and atomic systems. The characteristic feature of the
crystallization which occurs below the equilibrium freezing temperature is that the positional ordering
persists even after the shear is stopped. Here we demonstrate a novel shear-induced crystallization
phenomenon in a weakly swollen isotropic (L i ) and lamellar (L α ) mesophases with bilayers formed in a
cationic-anionic mixed surfactant system. Synchrotron rheological x-ray scattering reveals the transitions
to be 1st order and reversible under shear i.e., on stopping the shear, the crystalline phase Lc, reverts
back to the equilibrium mesophase. Rheo-optical observations show a shear-thickening which occurs
along with the preordering of L i phase induced by shear flow to L α phase before the nucleation of L c
phase. Shear diagram of the Li phase constructed in the parameter space of shear-rate () vs
temperature (T) exhibits L i L c + L i and L i L α + L i , transitions above the equilibrium crystallization
temperature (T K ), in addition to the irreversible shear-driven nucleation of L c in L i phase below T K .
Besides revealing a new class of non-equilibrium phase transitions, the present study urges a novel
approach towards understanding shear-induced phenomena in concentrated mesophases of mixed
amphiphilic systems.

Abstract
In Search for the Origin of Glassiness in La 0.85 Sr 0.15 CoO 3
Kaustuv Manna
Department of Physics, Indian Institute of Science, Bangalore- 560012, India
The magnetic behavior of La0.85Sr0.15CoO3 has been subjected to a controversial
debate for the last several years; while some groups show evidence for phaseseparation
(PS), others show spin-glass (SG) behavior. Here, we present a
comprehensive investigation of the structural, ac susceptibility, dc magnetization and
neutron diffraction studies on two sets of La0.85Sr0.15CoO3 polycrystalline samples
prepared from the same initial mixture but subjected to different heat treatment
processes. The dc magnetization study, done on both the samples show a kink in the
field-cooled magnetization and a peak in the zero-field-cooled magnetization which
shifts to the lower temperature at modest dc fields following an AT line behavior. In
addition, the ac susceptibility study exhibits a frequency dependent peak shift (~ 4 K)
which follows Volgel-Fulcher law, time-dependent memory effect, and a spin
relaxation time τo~10 -13 s; all of which strongly indicate the characteristics of the SG
behavior. The neutron depolarization measurement done on the conventionally
prepared La0.85Sr0.15CoO3 sample clearly shows the existence of ferromagnetic clusters
embedded in a non-ferromagnetic matrix. But, once the same sample is properly
homogenized by the repeated grinding and annealing process, these clusters
disappears and the sample turns to a pure SG phase with zero depolarization of the
transmitted neutron beam. Thus, our comparative study clearly reveals that the phaseseparated
nature is not intrinsic to La 0.85 Sr 0.15 CoO 3 system; in fact this is an outcome
of the compositional inhomogeneity. In essence, all the present experimental findings
evidence that the true ground state magnetic property of La0.85Sr0.15CoO3 is spin-glass
in nature.
References:
1. Kaustuv Manna, D. Samal, Suja Elizabeth, H. L. Bhat, and P.S. Anil Kumar
The Journal of Physical Chemistry C, (2011) 115, 13985-13990.
2. Kaustuv Manna, D. Samal, Suja Elizabeth, H. L. Bhat, and P.S. Anil Kumar
Journal of Superconductivity and Novel Magnetism, (2011) 24, 833–837.

Confinement of Spin Waves in Grids of Permalloy Nanowires
D. Venkateswarlu
Department of Physics, Indian Institute of Science, Bangalore 560012, India
Key words—electron beam lithography, shape anisotropy, nanowires, FMR, demagnetization fields, micromagnetics.
Recent advances in magnonics highlight its importance
in microwave frequency applications [1] . This involves the
use of spin waves for device applications. Here one needs
to look for better control over the spin waves and their band
structure [2-3] . The periodic variation in the effective
magnetic field in ferromagnetic materials is the basis for
the spin wave confinement and their propagation. Since the
effective field is the combination of exchange, external,
anisotropy and demagnetization (dipolar/ stray) fields; one
can achieve the periodic condition in many ways. In our
study, we employed geometry engineering by which the
shape anisotropy was tailored in obtaining the periodicity in
demagnetization fields. Soft magnetic material permalloy
(Ni 80 Fe 20 ) was made into grid like structure using a top
down approach.
Ferromagnetic resonance (FMR) measurements give the
information about the non travelling spin waves (k=0
modes). In general, one can see only single resonance
mode in FMR spectra in the case of thin films of permalloy.
This is due to its weak crystalline anisotropy even in
epitaxial conditions unlike the Fe thin films [4] . When the
permalloy film is made into nanowires with high aspect
ratio, it still gives the single mode but resonance condition
varies with applied field angles. This is due to the fact that
the shape anisotropy governs the condition for resonance.
This advantage of the shape anisotropy points towards the
usefulness of engineering the network structures.
Fundamentally one needs to understand the dynamics of
these network structures in order to meet the required
conditions for spin wave band structures in order to use
them in magnonics devices.
The grid structures were fabricated using electron beam
lithography followed by DC magnetron sputtering and liftoff
technique. The permalloy deposited on Si wafers was
20nm thick and is capped with 4nm gold to avoid
oxidation. The thickness of the deposited materials was
confirmed with the help of pre calibrated digital thinness
monitor. The lateral dimensions of the grid structures were
obtained using Scanning Electron Microscopy (SEM). The
permalloy wires in the grids found with widths about 140-
160nm. To understand the spin wave confinement effect
we varied the periodicities along horizontal and vertical
directions in the grid: (i) 560x560 (G1), (ii) 800x400 (G2)
and (iii) 1000x500 (G3) (all in nm units).
The FMR spectra on all the three grids were compared
with a reference sample, a continuous thin film grown
under same conditions during the fabrication. The
continuous film showed an uni-axial anisotropy. This was
induced due to the in-situ applied field during the growth.
But the magnitude is very small when compared to that of
structured samples. The quantitative comparison of
anisotropy constants was obtained with the help of fitting
done with theoretical equations involved in FMR
phenomena.
Two well resolved modes were observed in all three
grids whereas the reference sample gave only one mode.
These two modes corresponds to the spin waves confined
in horizontal and vertical sections of the grids. Spin wave
confinement was understood with the help of the mode
dependency on the in-plane angle of the applied magnetic
field with the grid. There were multiple peaks observed at
some angles in the G2, G3 which is not seen in G1.
The origin for these multiple peaks is understood with
the help of static micromagnetic simulations (MMS).
Dynamics of G1 using MMS followed by Discrete Fast
Fourier Transformations were used to correlate FMR
spectra. Our simulations methodology gave more insight
into the understanding of spin waves confinement. The
implementation of 2D-PBC [5] in our MMS made it possible
to study the real systems in realistic time.
Fig.1 Spin wave confinement in the horizontal and vertical
sections of the G1.
REFERENCES
[1] V. V. Kruglyak et al., J. Phys. D: Appl. Phys., vol. 43, p.
264001, 2010.
[2] Z. K. Wang et al., Acs Nano, vol. 4, p. 643, 2010.
[3] K. S. Lee et al., Phys. Rev. Lett., v. 102, p. 127202, 2009.
[4] S. Sakshath et al., J. Supercond. Nov. Magn.,
DOI:10.1007/s10948-011-1269-3
[5] D. Venkateswarlu et al., IEEE Trans. Magn., vol. 48, no.
11, Nov. 2012.
FMR experiments were done in collaboration with Prof. S. V. Bhat
D.Venkat@physics.iisc.ernet.in

Magnetohydrodynamic stability of stochastically driven accretion
flows
Sujit Kumar Nath 1 , Banibrata Mukhopadhyay 1 , Amit K. Chattopadhyay 2
1. Department of Physics, Indian Institute of Science, Bangalore 560 012, India;
sujitkumar@physics.iisc.ernet.in ; bm@physics.iisc.ernet.in
2. Aston University, Non-linearity and Complexity Research Group, Engineering
and Applied Science, Birmingham B4 7ET, UK; a.k.chattopadhyay@aston.ac.uk
Abstract
We investigate the origin of magnetohydrodynamic turbulence in rotating shear flows. The
particular emphasis is the flows whose angular velocity decreases but specific angular momentum
increases with increasing radial coordinate. Such flows, which are extensively seen in astrophysics,
are Rayleigh stable, but must be turbulent in order to explain observed data. The present work
explores the effect of stochastic noise on such magnetohydrodynamic flows. We essentially concentrate
on a small section of such a flow which is nothing but a plane shear flow supplemented
by the Coriolis effect. This also mimics a small section of an astrophysical accretion disk. It is
found that such stochastically driven flows exhibit large temporal and spatial correlations of perturbation
velocities, and hence large energy dissipations of perturbation increasing indefinitely with
time, which presumably generates instability. A range of specific angular momentum (λ) profiles,
as functions of radial coordinate of background flow, starting from Keplerian to constant specific
angular momentum is explored. However, all the background profiles exhibit identical growth and
roughness exponents with similar amplitude of perturbations of energy, revealing a unique universality
class for the stochastically forced magnetohydrodynamics of rotating shear flows. This work,
is an attempt to understand origin of instability and turbulence in the three-dimensional Rayleigh
stable rotating shear flows. This has important implications to resolve the turbulence problem in
astrophysical magnetohydrodynamic flows such as accretion disks.

Flow Enhanced Pairing and Other Stories
of fermions in synthetic gauge fields
Vijay B. Shenoy
Centre for Condensed Matter Theory
Indian Institute of Science, Bangalore 560 012
shenoy@physics.iisc.ernet.in
In this talk, intended for a broad audience, I will describe our recent work on
interacting fermions in synthetic non-Abelian gauge fields. A uniform non-Abelian
gauge field, such as those proposed and realized in cold-atom systems, produces a
generalized Rashba spin-orbit interaction that influences the motion of the fermions. I
will show that this system contains rich and novel physics whose significance extends
from high temperature superconductivity to quantum computing. A novel feature
uncovered in our most recent work is the phenomenon of flow enhanced pairing
apparently contradicting Landau who argues that flow is detrimental to pairing.
Reference on flow enhanced pairing: 1211.1831. I thank J. P. Vyasanakere for
comments and criticisms, and DAE/DST for generous support of this work.

A Unique Electrical switching behavior in Cu-As-Se glasses
K. Ramesh
Department of Physics, Indian Institute of Science, Bangalore 560012, India.
ABSTRACT
A unique electrical switching behaviour has been observed in Cu x As 40 Se 60-x glasses over
a wide range of composition (0 ≤ x ≤ 32). The glasses with lower Cu concentrations (x < 15) do
not exhibit switching, whereas glasses in the range 15 ≤ x ≤ 25 show a threshold type switching.
The glasses in the range 25 ≤ x ≤ 28 exhibited an unusual switching from low resistance to high
resistance state. For x ≥ 30, the glasses are found to show a memory switching. This is a unique
observation and for the first time a system showing no switching → threshold switching → low
resistance to high resistance switching
→
memory switching has been observed.
The thermal crystallization of Cu x As 40 Se 60-x glasses at their respective crystallization
temperatures indicate that the structural network is mainly characterized by Cu 3 AsSe 4 and
As 2 Se 3 for x < 15 and by Cu 3 AsSe 4 and Cu 2 As 3 for x ≥ 25. The composition range 15 ≤ x ≤ 20 is
characterized only by Cu 3 AsSe 4 structural units. The samples cooled from their melt show only
the ternary Cu 3 AsSe 4 for x ≤ 20. For x > 20, precipitates of ‘As’ has also been observed along
with Cu 3 AsSe 4 and Cu 2 As 3 phases.
Normally, the memory switching is explained with the thermal model and threshold
switching is explained with the electronic model. The present studies provide a unique way to
understand the electrical switching exhibited by chalcogenide glasses based on the thermal mode
and filament formation. The proposal of the influence of cross-linking and rigidity of the
structural network in changing the switching type from memory to threshold and vice versa is
also ruled out by the present studies.

Heteronuclear Double Quantum Correlation Experiments
Involving Protons for the study of Partially Ordered and
Rigid Systems
Y. Jayasubba Reddy a,b and K.V. Ramanathan a
a NMR research Center, Indian Institute of Science Bangalore-560012, India
b Departmment of Physics
The current objective of our research is to develop and apply high resolution solid state NMR
methods to study the intermolecular interactions and 3D molecular structure of small molecules
(like drugs, tri and octa peptides and thermotropic liquid crystals) at isotopic natural abundance.
1 H NMR chemical shifts and dipolar couplings are the powerful probe for intermolecular
interactions, more specifically H-bonding, cis-trans conformation, π-π interactions and
dimerization, which control the self assembly of molecules in the solid state.
While considering all these advantages we have utilized 1 H based heteronuclear correlation
experiments. Multiple quantum correlation spectroscopy in the case of rigid and semi rigid
systems can provide useful proximity information, as the coherences can be generated between
dipolar coupled spin systems. Here we present our efforts in utilizing proton double quantum and
carbon single quantum correlation experiments for the case of static oriented liquid crystal
samples and rigid biological samples. Correlations based on both scalar and dipolar couplings are
being explored. Examples of studies with some proline based tripeptides which exhibit cis-trans
isomerism, thiophene based systems and a liquid crystalline material will be presented. To
confirm the resonance assignments, we have also used the GIPAW module contained in the open
source Quantum Esspresso (QE) code and chemical shifts with reasonable agreement with
experiment have been obtained.

Self-propelled granular rod amid a noisy medium: An experimental test
of Isometric Fluctuation-Relation
Nitin Kumar*, Sriram Ramaswamy and A.K. Sood
Department of Physics, Indian Institute of Science, Bangalore-560012, India.
Abstract
We provide an experiment to examine Isometric Fluctuation Relation (IFR) [1] which relates the
relative probabilities of two isometric current vectors pointing in different directions in d-
dimensional space. The experiment consists of a self-propelled granular rod moving amidst a
noisy medium of spherical particles on a two dimensional surface. We analyse its two
dimensional velocity vector field (V) and show that IFR is indeed valid but only at “higher”
velocities whose magnitude is greater than transverse width of velocity distribution at V = 0.
Using IFR, we confirm that Gallavotti-Cohen Fluctuation Relation (GCFR) can be obtained as a
special case when velocity vectors are pointing in opposite directions [2]. Moreover using IFR
we show that GCFR is valid even when current fluctuations are oblique to the propulsive force.
We compute the Large Deviation Function (LDF) which is very different from paraboloid
signifying that system obeys IFR even when the fluctuations are non-Gaussian.
References:
[1] P. I. Hurtado et al., PNAS 108, 7704 (2011)
[2] Nitin Kumar, Sriram Ramaswamy and A. K. Sood, Phys. Rev. Lett. 106,118001 (2011).
_____________
*electronic mail: nksharma@physics.iisc.ernet.in

Probing superconductivity in the 2D limit using resistivity noise
R.Koushik 1 , Mintu Mondal 2 , John Jesudasan 2 , Pratap Raychaudhuri 2 , Aveek Bid 1 and Arindam Ghosh 1
1
Department of Physics, Indian Institute of Science, Bangalore 560012, India
2
Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India
Superconductivity in low dimensions has invoked lot of interest in recent times with the advent of new materials
like topological superconductors, electron gas at oxide interface etc. In 2D, the superconducting transition is
known to occur via Berezenskii Kosterlitz Thouless (BKT) phase transition. Conventional techniques like
resistivity measurements, superfluid density measurements, IV characteristics are generally used to study the
nature of transition (BKT or BCS). But their sensitivity is limited as inhomogeneity can smear out signatures of
BKT transition.
In this work, we use the higher order statistics of resistivity fluctuations to address the nature of superconducting
transition in ultra thin films of Niobium Nitride. Our technique involves detecting non-Gaussian component (NGC)
in fluctuations which are sensitive to long- range correlations in the system. The measure of NGC is given by
second spectrum (equivalent to kurtosis). We find strong non-Gaussian fluctuations closer to the transition
temperature (T KT) in films exhibiting BKT transition which monotonically decrease with increase in temperature
and reduces to background level as the mean field temperature is approached (T BCS). The NGC is completely
absent in bulk films. We attribute the NGC to the presence of long-range interaction between vortices which
naturally occur in a BKT transition whereas the Ginzburg Landau (GL) fluctuations occuring in bulk films are
Gaussian in nature.
Our experiments underline a new method to identify the characteristic temperature scales of phase fluctuations
in the superconducting state, that can be useful to probe other low dimensional superconductors as well.
Key words: Non Gaussian, Kosterlitz-Thouless transition
References
1. R. Koushik et al., (under preparation)
2. Mintu Mondal et al., Phys. Rev. Lett 107, 217003 (2011)

TITLE: NUCLEOSYNTHESIS INSIDE GAMMA­RAY BURST ACCRETION DISKS
AND ASSOCIATED OUTFLOWS
AUTHORS: Indrani Banerjee, Banibrata Mukhopadhyay
Department of Physics, Indian Institute of Science, Bangalore­560012
ABSTRACT
Most popular models of long duration gamma­ray bursts invoke the core collapse of
rapidly rotating stars. The mass of the stars undergoing core collapse is usually
greater than 20 solar mass in the main sequence. This core collapse results in the
formation of black holes of 2­3 solar masses if it is of Schwarzschild type and 6­7
solar masses if it is of maximally spinning Kerr type with an accretion disk around
them. Such black holes accrete at the rate of 0.001­10.0 solar masses per second. We
investigate nucleosynthesis inside such gamma­ray burst accretion disks with
accretion rate upto 0.1 solar mass per second since these disks are more likely to
synthesize heavy elements. We show that varying accretion rate changes the
nucleosynthesis products. We also report how nucleosynthesis is sensitive to the
variation of the initial abundance of elements in the accretion disk, namely whether it
is Si rich or He rich. In addition to the formation of various isotopes of Fe, Co and Ni
we report the synthesis of new elements like Ar35, F21, Mn53 and various isotopes of
Cr which have not been reported earlier. Next, we investigate whether these elements
survive in the outflows from the disk and we find that the result is sensitive to the
fraction of mass ejected to the mass accreted and hence to the velocity of ejection.
When the velocity of ejection is small we find that many new elements like isotopes of
Ti, V, Cu and Zn are synthesized. We also give a rough estimate of the change in the
mass fraction of a particular species due to these core collapse events during the
lifetime of a galaxy, which affects the metallicity of the universe. Many of these
elements thus synthesized have been observed in the X­ray afterglows of several
gamma­ray bursts.

Freezing of the octahedral tilt near ferromagnetic transition and appearance of a glassy
phase at low temperature driven by the tilt instabilities in SrRuO 3
Chanchal Sow
Department of Physics, Indian Institute of Science, Bangalore 560012, India
SrRuO 3 is a well known itinerant ferromagnet with many intriguing characteristics. Here we
present a critical investigation on the structural, magnetic, and magnetotransport properties of
polycrystalline SrRu (1-x) O 3 (0.07 < x < 0) samples with uniquely defined ferromagnetic transition
temperatures. The ac magnetic susceptibility study exhibits the remarkable memory effect, a
distinct characteristic of glassy behavior, at low temperatures. The transport study suggests a
crossover from Fermi-liquid to non-Fermi-liquid behavior. Most strikingly, the temperaturedependent
magnetoresistance reveals the possibility for an additional magnetic ordering (apart
from ferromagnetic) by demonstrating a peak in magnetoresistance at the low temperature side
as well. In addition, the temperature-dependent coercive field shows a plateau around 50 K. In
order to understand the genesis of such unusual low-temperature magnetic features, we have
undertaken a detailed temperature dependent (5-250 K) neutron diffraction study. We observe a
freezing of the octahedral tilt near the ferromagnetic transition and unusual changes in the
structural parameters (unit-cell lattice parameters, octahedral tilt etc.) near the onset of low
temperature spin glass like phase. A reduction of the ordered magnetic moment and a decline in
the total integrated magnetic intensity is also observed around the same temperature. Hence it is
believed that the low-temperature anomalous magnetic response is closely intertwined to the
lattice-parameter change.
Reference:
[1] C. Sow, D. Samal, P. S. A. Kumar, A. K. Bera, and S. M. Yusuf, Phys. Rev. B 85, 224426
(2012).
[2] C. Sow, D. Samal, and P. S. A. Kumar, J. Appl. Phys. 111, 07E121 (2012).

Single-particle and collective behaviour of
colloidal swimmers
Suropriya Saha, Sriram Ramaswamy, Ramin Golestanian
November 16, 2012
Colloidal particles with a catalytic region on their surface, when immersed in
areactantsolution,generateachemicalgradientintheirownvicinity[1],anduse
the resulting anisotropic stresses to propel themselves through the mechanism of
diffusiophoresis. We have have shown that polar active particles of this type can
alsoorientthemselvesalonganimposedgradientofreactantconcentration. This
amounts to a theoretical demonstration of a phoretic analogue of chemotaxis,
that is, the ability of a self-propelled particle to align with respect to, and hence
to move up or down, a chemical gradient. The nature of the chemotaxis depends
on the shape of the particle, on the distribution of enzymatic sites on its surface,
and on the surface mobility. We have also shown that a collection of these
particles when supplied with reactants at a steady rate can interact through
their long ranged diffusion fields to produce clumping or patterning instabilities.
We have studied these instabilities by looking at the mode structure and the
structure factor in different limits – abundant or meagre supply of reactants and
slow or fast reaction dynamics.
References
[1] R. Golestanian, T. B. Liverpool and A. Ajdari, Phys. Rev. Lett. 94, 220801
(2005)
1

POSTER
ABSTRACTS

Titile: Study of switching field statistics of Permalloy (Ni 80 Fe 20 ) Hall bars by planar Hall effect
Author: Arnab Roy
Planar Hall effect was used to study the switching behaviour of 1mm*100µm*15nm permalloy
(Ni 80 Fe 20 ) Hall bars grown in (111) orientation on Si(100). Reversal model was Arrhenius type
activation over energy barriers,
−∆E
( H )
kBT
. Statistical analyis of the field-driven magnetization
p(
H ) = e
reversal process was carried out by studying the switching field for a large number of magnetic field
cycles beween ±20Oe. A potrtion of a few typical hysteresis curves is shown in figure 1.
⎛ H ⎞
The model proposed by M.P.Sharrock[1] : ∆ E( H ) = KV
⎜1
−
H
⎟ with H O =2xK/M was used to find
⎝ 0 ⎠
the shape of the energy landscape for the bar undergoing reversal in an applied field. Multiple
reversal paths were observed for a given wire under the same conditions(figure 2), each distribution
in very good agreement with the above model, allowing the calculation of :
1. Temperature dependence of the effective anisotropy constant for the bar; K(T)= (1/2)*H o M(T)
(x=1 for applied field at 0 O )
2. Energy barrier landscape: An exponent m= 1.5 to 2 is expected to leading order in the expansion
of the energy barrier according to the Stoner Wolfarth model, however, our results give an exponent
of 2.8 to 3 for all angles (out of plane) of the applied field for the principal reversal path, pointing to
mechanisms other than coherent rotation at work. If domain wall propagation and pinning is the
mechanism of reversal, this study determines the energy landscape around the pinning field.
m
-2.0x10 -5
120
-2.5x10 -5
100
Hall voltage (V)
-3.0x10 -5
No. of Reversals
80
60
40
-3.5x10 -5
20
0
-4.0x10 -5
3 4 5 6 7
H(Oe)
3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0
H(Oe)
Figure 1. Figure 2.
References:
[1] M.P.Sharrock, J. Appl. Phys. 76, 6413 (1994);

Unzipping Force Analysis to determine binding specificity of
RNA Polymerase to T7A1 promoter sequence
Sudeesh K †,1 , Subho Ghosh* ,1 , Dipankar Chatterji*, A K Sood †
† Department of Physics, Indian Institute of Science
* Molecular Biophysics unit, Indian Institute of Science
Abstract:- Transciption is one of the important steps in the central dogma of molecular biology. Using
RNA Polymerase of Escherichia coli and T7A1 promoter from T7 phage as the model system, we
probe the sequence dependence of the unzipping force of transcription at the single molecule level. We
unzip wild type and various mutated sequences of DNA with RNA-polymerase attached to each of
them and determine the change in the binding force at the beginning of the unzipping of the
transcription bubble. We thus determine the role of each individual base pair of the consensus
promoter sequence affecting the binding of RNA-Polymerase to the promoter.
1) S.K and S.G contributed equally for the work

Why does sun occasionally stop giving sunspots for several years?
Bidya Binay Karak & Arnab Rai Choudhuri
One of the most striking aspects of the 11-year sunspot cycle is that there have been times in the past
when some cycles went missing. A most well-known example of this is the Maunder minimum in 17 th
century when sunspots disappeared for about 70 years. Analyses of cosmogenic isotopes (C14 and
Be10) indicate that there were about 27 grand minima in the last 11,000 yr. This implies that about 2.7
of the solar cycles had conditions appropriate for forcing the Sun into grand minima. We address the
question how grand minima are produced and specifically calculate the frequency of occurrence of
grand minima from a theoretical model. With reasonable assumptions we show that a dynamo model
leads to the conclusion that about 1-4% of the sunspot cycles may have conditions suitable for inducing
grand minima.

Can interaction between emergent excitations be independent of
the constituent interactions?
Jayantha P. Vyasanakere ∗ and Vijay B. Shenoy †
Centre for Condensed Matter Theory, Department of Physics,
Indian Institute of Science, Bangalore 560 012, India
(Dated: November 16, 2012)
Abstract
Normally, in condensed matter systems, the interaction between emergent excitations will depend
on the interactions among their constituents. For example, magnon-magnon interaction depends
on the exchange interaction between the spins. Here we illustrate a novel system in which this is
not the case.
We had recently shown that a non-Abelian gauge field induces a BCS-BEC crossover in a weakly
interacting fermionic system. We also showed that the BEC thus obtained is a condensate of novel
kind of bosons called rashbons, which are fermion-dimers. Here we study this system by constructing
a Gaussian theory of quantum fluctuations and show that the rashbon-rashbon interaction is
independent of the interaction between the constituent fermions. In fact, the rashbon-rashbon interaction
depends solely on the rashba spin-orbit coupling induced by the non-Abelian gauge field,
which enters the kinetic energy term in the Hamiltonian.
This is, to the best of authors’ knowledge, a unique and an interesting state in any condensed
matter system.
Research funding: CSIR, DST, DAE.
References : arXiv: 1201.5332, 1108.4872, 1104.5633.
1

Can interaction between emergent excitations be independent of
the constituent interactions?
Jayantha P. Vyasanakere ∗ and Vijay B. Shenoy †
Centre for Condensed Matter Theory, Department of Physics,
Indian Institute of Science, Bangalore 560 012, India
(Dated: November 16, 2012)
Abstract
Normally, in condensed matter systems, the interaction between emergent excitations will depend
on the interactions among their constituents. For example, magnon-magnon interaction depends
on the exchange interaction between the spins. Here we illustrate a novel system in which this is
not the case.
We had recently shown that a non-Abelian gauge field induces a BCS-BEC crossover in a weakly
interacting fermionic system. We also showed that the BEC thus obtained is a condensate of novel
kind of bosons called rashbons, which are fermion-dimers. Here we study this system by constructing
a Gaussian theory of quantum fluctuations and show that the rashbon-rashbon interaction is
independent of the interaction between the constituent fermions. In fact, the rashbon-rashbon interaction
depends solely on the rashba spin-orbit coupling induced by the non-Abelian gauge field,
which enters the kinetic energy term in the Hamiltonian.
This is, to the best of authors’ knowledge, a unique and an interesting state in any condensed
matter system.
Research funding: CSIR, DST, DAE.
References : arXiv: 1201.5332, 1108.4872, 1104.5633.
1

High mobility graphene devices
Paritosh Karnatak, T Phanindra Sai, Srijit Goswami, Subhamoy Ghatak, Arindam Ghosh
Department of Physics, Indian Institute of Science, Bangalore-560012
Graphene being a single atomic layer is significantly affected by the substrate, as the
intrinsic properties of graphene are often masked in the presence of disorder. It is well known
that the presence of substrate trap charges, polar phonons, roughness and ripples collectively
hinder studies on ultrahigh quality graphene. It was also predicted that if the effect of such
external disorder could be eliminated, graphene would show extremely high mobility.
Here we report the methods followed in making high mobility graphene devices. One of
the ways to achieve high mobility is by etching out the substrate underneath the graphene. In
such suspended graphene devices we have achieved mobilities of ~150,000 cm 2 /V-s. Such
devices are potential candidates to explore new physics and may find viable applications as
sensor devices. Another approach to produce high mobility graphene is to transfer graphene on
to thin flakes of hexagonal boron nitride, which has a similar arrangement of atoms as graphite.
Boron nitride flakes are found to be atomically flat, do not contain dangling bonds or traps. The
result is that graphene on boron nitride has significantly higher mobilities ~50,000 cm 2 /V-s,
which is significantly higher than the common graphene/SiO 2 /Si system. In addition, these
systems are mechanically more stable than suspended graphene structures, and open up the
possibilities of designing more intricate device structures.

Measurement of Proton-Carbon Dipolar Couplings using an
improved DAPT pulse sequence
R.V. Sudheer Kumar $, # and K.V. Ramanathan #
Department of Physics $ , NMR research centre #
Indian Institute of Science, Bangalore, India
Dipolar couplings provide valuable information on order and dynamics of liquid crystals.
Experiments to measure heteronuclear dipolar couplings are very powerful and widely
important in solid state NMR, since it provides site specific dipolar couplings in aligned
samples. Interpretation of these heteronuclear dipolar couplings are hampered by the
chemical shift anisotropy (CSA) and dipolar interactions among abundant spins ( 1 H- 1 H
couplings). Additionally, multiple 13 C- 1 H dipolar couplings found in complicated systems
make the spectra more difficult to use. For static samples the complications are resolved
partially by separated local field (SLF) spectroscopy where the local field due to
heteronuclear dipolar coupling and chemical shift interactions are separated into two
frequency domains in a 2D experiment. A method of separated local field experiment is
presented for measuring heteronuclear dipolar couplings in oriented systems. This method is
based on Dipolar assisted polarization transfer (DAPT). Compared to rotating frame
techniques based on Hartmann-Hahn match, this approach is easy to implement and is
independent of any matching condition. DAPT can be utilized either as a proton encoded
local field (PELF) technique or as a separated local field (SLF) technique, which mean s that
the heteronuclear dipolar coupling can be obtained by following either evolution of the
abundant spin like proton (PELF) or that of the rare that of carbon (SLF).The DAPT pulse
sequence has been improved for efficient homonuclear decoupling by the interpretation of
BLEW-48 pulse sequence. The implementations of the modified DAPT experiment both as a
PELF and as SLF on oriented liquid crystalline samples have been carried out. The
performance of this experiment is compared with PISEMA.

Ultrafast NMR Techniques in Inhomogeneous Magnetic Fields
KowsalyaDevi Pavuluri $, # and K. V. Ramanathan #
Department of Physics $ , NMR Research Centre #
Indian Institute of Science, Bangalore
Nuclear Magnetic Resonance (NMR) enables one to probe the structure and dynamics of
matter in non-invasive manner. A major limitation of NMR for getting high resolution is the
requirement of strong and extremely homogeneous magnets. Portable NMR systems have
been built with open single sided probes for studying objects or samples whose size is limited
to fit inside the bore of the magnet. But their use remained mainly for product and quality
control since spectroscopic information cannot be recovered due to very large
inhomogeneities. Nutation echo is one of the novel techniques where RF field gradients and
static field gradients are matched to refocus static inhomogeneities but the full chemical shift
information is maintained. Multidimensional NMR experiments can be designed based on
nutation echo to get structural information in presence of inhomogeneous magnetic fields.
But multidimensional NMR experiments are inherently multi scan in nature and rely on a
series of independent acquisitions to sample the spin evolutions throughout the indirect time
domains. Spatial encoding technique enables the collection of complete multidimensional
NMR data sets in single scan. Designing experiments based on nutation echo and spatial
encoding can provide high resolution NMR spectra in inhomogeneous magnetic fields with in
fraction of a second. In this presentation, results of a 2D experiment obtained using spatial
encoding is presented. Possibilities of using this approach in the presence of inhomogeneous
magnetic fields will be discussed.
References:
1. Carlos A. Meriles et.al Science 293, 82-85 (2001).
2. Henrike Heise et.al J. Magn. Reson. 156, 146-151 (2002).
3. Y.Shrot, Lucio Frydman J. Chem. Phys. 128, 052209 (2008)

Low temperature electrical transport studies on carbon nitride
films prepared by chemical vapour deposition
M. Prashantha, E.S.R. Gopal and K. Ramesh ∗
Department of Physics, Indian Institute of Science, Bangalore 560012, India.
The search for new materials for advanced application leads to the discovery of new materials
with interesting electrical, physical, chemical and mechanical properties. The advancement of
society and quality of human life also depends on these advanced materials. In this aspect
carbon nitrides have been predicted to have high hardness, high wear resistance with low
friction coefficient. These properties make them as a promising material for various
applications such as organic semiconductors, fuel cells and photocatalysis, mechanical cutting
tools, protective coatings, biomedical applications, electroluminescence devices, optical
materials etc. The coating can reduce the wear, friction and corrosion, which can increase the
life time and efficiency of the high speed moving parts. Carbon nitride coating is also found to
be biocompatible. So, the successful synthesis of carbon nitride would have an enormous
impact not only on the basic science but also on the technological development.
In this work, we have attempted to prepare carbon nitride by chemical vapour deposition
(CVD). We have used Azabenzimidazole (C 6 H 5 N 3 ) as the precursor which has both carbon
and nitrogen bonding in its structure. In a two zone furnace, the vapours of the precursor
evaporated at 450 o C in Zone I are made to enter into Zone II which is kept at high
temperature. The vapours get pyrolysed and deposit on quartz and silicon substrates. The
samples were prepared at different pyrolysis temperatures of 725, 750, 775, 800 and 825 o C.
As the C-N bond is significantly strong, even at high temperatures a considerable amount of
C-N bonding is retained. This method is simple and enables one to have control over the
amount of nitrogen in the system by controlling the pyrolysis temperature, volume of the
liquid and the process time. The concentrations of N decreases gradually from 26 to 20 at %
for the films prepared at pyrolysis temperatures of 725 to 825 o C.
Electrical transport studies at low temperature (RT to 4.5K) show that the carbon nitride films
exhibit Metal-Insulator (MI) transition. The incorporation of nitrogen into carbon introduces
disorder in the structure. The disorder increases with the decrease of the nitrogen content,
greatly influences the electrical transport properties. Disorder induced metal-insulator
transitions are well known and can be studied by varying the temperature, pressure, doping
level etc. In present study, metal insulator transition exhibited by carbon nitrides prepared at
different pyrolysis temperatures has been studied. It is observed that the increase in pyrolysis
temperature shifts the MI transition temperature to lower values. The transition temperatures
for the samples prepared at 725 o C, 750 o C and 775 o C are 84.7 K, 67.7 K and 9.5 K
respectively. The reduced activation energy indicates that the metallic regime of the samples
prepared at pyrolysis temperatures > 800 o C lies at low temperatures. It is also observed that
the activation energy decreases with the increase in pyrolysis temperature.
∗ Corresponding author: kramesh@physics.iisc.ernet.in
1

Investigating DNA hybridization through changes in
conductance of ultrathin Au nanowires
Nidhi Lal 1 , Avradip Pradhan 2 , Arindam Ghosh 2 and N. Ravishankar 1
1 Materials Research Centre, Indian Institute of Science, Bangalore 560012, India
2 Department of Physics, Indian Institute of Science, Bangalore 560012, India
DNA hybridization is a biological process which is unique in being extremely specific
where nucleotides in one strand bind to their counterpart in the other strand via
hydrogen bonds. DNA molecules also carry negative charge and thus have the potential
to change the conductivity of various nanostructures when bound to them. We have
used the very same property of these molecules to identify the process of DNA
hybridization by changing the conductivity of ultrathin Au nanowires. Label free electrical
detection of DNA hybridization has been studied using various nanostructures (CNTs,
silicon nanowires and graphene, for instance). In the present study, single stranded
DNA (ssDNA) molecules were immobilized over Au nanowires. The immobilization was
confirmed by AFM characterization done on ssDNA attached to Au nanowires. Upon
addition of target molecules, a significant change in the conductance of Au nanowires
was observed. These measurements were carried out by two probe resistance method
done at room temperature.

Quantum Simulation of Dzyaloshinsky-Moriya Interaction
V. S. Manu and Anil Kumar
Centre for Quantum Information and Quantum Computing,
Department of Physics and NMR Research Centre, Indian Institute of Science, Bangalore-560012
Quantum simulation of a Hamiltonian H requires unitary operator decomposition (UOD) of
its evolution operator, (U = exp(−iHt) ) in terms of experimentally preferable unitaries. Here, using
Genetic Algorithm optimization, we numerically evaluate the most generic UOD for the
Hamiltonian, DM interaction in the presence of Heisenberg XY interaction, H DH . Using these
decompositions, we studied the entanglement dynamics of Bell state in the Hamiltonian H DH and
verified the entanglement preservation procedure by Hou et al.[1].
References:
1. Y.C. Hou, G.F. Zhang, Y. Chen, and H. Fan. Preservation of entanglement in a two-qubit-spin
coupled system. Annals of Physics, 327:292296, 2012.

Title : Measurement of Forces applied by C. elegans moving on Agarose surfaces.
Authors: Siddharth Madhav Khare*, Prof. V. Venkataraman*, Prof. Sandhya P. Koushika#
* Department of Physics, IISc Bangalore #TIFR, Mumbai
Abstract:
The technique of using flexible micropillars as force sensors has already been used to probe a
wide range of forces in the range of piconewtons to micronewtons. Micro-pillars made of SU8
have been used by Doll et. al. 1 to measure force exerted by C. elegans moving on agar pieces.
Force pattern of moving C. elegans using poly Dimethyl Siloxane(PDMS) pillar arrays has been
recorded by A. Ghanbari et.al. 2
In the present work we use a similar technique. We fabricate micropillars of PDMS using
photolithography on SU8 followed by replica molding. Pillar height is maintained at
134(±10.78)µm and diameter is maintained at 48(±1.73) µm. Inter pillar distance is 50µm.
Stiffness of the pillar is calculated to be 1.01µN/µm. 2 Force patterns of C. elegans wild type and
touch defective animals have been recorded. Our device geometry is simple to fabricate, easy to
handle and easy to use. We are attempting to determine whether different mutants of C. elegans
generate different forces during locomotion. C. elegans strains N2 have been shown to move
faster than mec-4(e1339) and mec-10(e1515) in periodic agar structures by Park et.al. 4
Our device is capable of combining force measurement with the artificial soil like environment. 3
References:
1. Joseph C. Doll, Nahid Harjee, Nathan Klejwa, Ronald Kwon, Sarah M. Coulthard, Bryan Petzold, Miriam
B. Goodman and Beth L. Pruitt, Lab Chip, 2009, 9, 1449–1454
2. Ali Ghanbari, Volker Nock, Shazlina Johari, Richard Blaikie, XiaoQi Chen and WenhuiWang, J.
Micromech. Microeng. 22(2012) 095009
3. S. R. Lockery, K. J. Lawton, J. C. Doll, S. Faumont, S. M. Coulthard, T. R. Thiele, N. Chronis, K. E.
McCormick, M. B. Goodman, and B. L. Pruitt, J Neurophysiol 99: 3136–3143, 2008.
4. Sungsu Park, Hyejin Hwang, Seong-Won Nam, Fernando Martinez, Robert H. Austin, William S. Ryu,
PLoS ONE 3(6): e2550. doi:10.1371/journal.pone.0002550

Low frequency noise in Topological Insulator Bi 1.5 Sb 0.4 Te 1.7 Se 1.3
Semonti Bhattacharyya, Mitali Banerjee, Hariharan N, Saurav Islam
Suja Elizabeth and Arindam Ghosh
Department of Physics, Indian Institute of Science, Bangalore 560012
ABSTRACT
Topological insulator is a new quantum state of matter which exhibits exotic metallic surface states in the
bulk insulating band gap. These surface states are protected from back scattering by high spin-orbit
coupling and time reversal symmetry. Probing these surface states using electrical transport measurement
is a challenging task because of natural bulk doping present in the crystals caused by defects or
imperfections (Se vacancies in case of Bi 2 Se 3 and antisite defects in case of Bi 2 Te 3 ). Bi 1.5 Sb 0.4 Te 1.7 Se 1.3 has
proved to be one of the best compositions to achieve maximal surface transport as donors and acceptors
compensate each other in this material (1). We have studied electronic transport in mechanically
exfoliated thick (~150 nm) and thin (>15 nm) flakes of Bi 1.5 Sb 0.4 Te 1.7 Se 1.3. For thick crystals the
temperature dependence of resistance shows activated-type behavior whereas for thin crystals it shows
metallic behavior. It is also observed that in thick crystals the resistance starts saturating at 50 K
indicating the onset of surface transport. The magnitude of “1/f” noise in these thick samples decreases in
the temperature range between 200K to 80 K; then it starts increasing and finally reaches a maximum at
~18K.This data suggests that “1/f” noise can be used as an important tool to identify the contribution of
surface states in electronic transport. The gate voltage dependence of noise shows that the noise
magnitude also increases with decreasing carrier density. For thin samples the magnitude of 1/f noise
increases at lower temperatures and with decreasing carrier densities.
1. PHYSICAL REVIEW B84, 165311 (2011)
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Superconducting fluctuations, Anomalous Phonons and
Electronic excitations in iron-based superconductors
Pradeep Kumar, A. Bera, D. V. S. Muthu and A. K. Sood
Department of Physics, Indian Institute of Science, Bangalore, India
We will present our recent Raman studies on iron-based superconductors (FeBS) as a
function of temperature. In Ca 4 Al 2 O 5.7 Fe 2 As 2 superconductor, our spectroscopic studies
reveal that the phonon mode observed at ~ 230 cm -1 shows a jump in frequency by ~ 2 %
and linewidth increases by ~ 175 % at T o ~ 60 K. Below T o, anomalous softening of the
mode frequency and a large decreases by ~ 10 cm -1 in the linewidth are observed. These
precursor effects at T 0 ( ~ 2T c ), seen for the first time in FeBS, are attributed to
significant superconducting fluctuations possibly arising from a reduced coupling
between the two well separated ( ~ 15 Å ) Fe-As layers in the unit cell. Furthermore, a
large blue-shift of the mode frequency between 300K and 60K ( ~ 7% ) indicates strong
spin-phonon coupling [1].
In case of the 122 system i.e. Ca(Fe 0.97 Co 0.03 ) 2 As 2 , all three observed phonon mode show
strong renormalization effects below the structural as well as magnetic transition
temperature (T SM ~ 160K ) attributed to the spin-phonon and electron-phonon coupling.
We observed four very weak modes in the range 400-1000 cm -1 attributed to the
electronic Raman scattering. In addition, we have observed a broad Raman band
centering at ~ 3200 cm -1 signaling the existence of coupled orbital and magnetic
excitations owing to its anomalous temperature dependence [2].
We thank all our coauthors mentioned in the references below.
Reference:
[1] Pradeep Kumar et al., Appl. Phys. Lett. 100, 222602 ( 2012).
[2] Pradeep Kumar et al., To be submitted.

Molecular dynamics simulation of electroporation of lipid bilayer membrane
Amit Kumar Majhi, V. Venkataraman, Prabal K Maiti
Department of Physics, Indian Institute of Science Bangalore, India, 560012.
Abstract
MD Simulation [1] has been performed using NAMD and VMD [2-4] to determine the pore
formation time scale for different applied fields and analyzed the movement of ions across the
electroporated lipid bilayer membrane. In addition, we have also studied the closing dynamics of
a pore when the field is switched off. The MD simulation has been performed for a total of 100
ns in presence of KCl solution of 0.2 M concentration in the water layer with different electric
fields ranging from 0.2 V/nm to 1 V/nm to elucidate the pore formation mechanism. The field is
always applied along the z-axis (perpendicular to the lipid layer) after 4 ns of equilibration. We
find that a pore formation starts at different time depending on the strength of applied fields. For
example, the pore formation starts 1ns after the application of an electric field of 0.4 V/nm but
for a field of 1V/nm pore formation starts after 0.2ns. Once a pore appears on the membrane it
expands quickly but if the field is switched off the pore reseals back but at slower speed. We
have also calculated ionic current as a function of time for different applied fields. When the
field is just turned on, the current does not flow at all but after some time it increases sharply.
This sharp rise coincides with the formation of the pore. The magnitude of the ionic current
through the membrane is found to be 10-20 nA. Pore formation mainly depends on the
magnitude of the field which indicates the increase in conductivity of the membrane with
application of electric field.
References:
1. Low voltage irreversible electroporation induced apoptosis in HeLa cells,. Wei Zhou, Zhengai
Xiong, Ying Liu, Chenguo Yao, Chengxiang Li,. 2012, DOI:10.4103/0973-1482.95179.
2. Scalable molecular dynamics with NAMD. J. C. Phillips, R. Braun, W. Wang, J. Gumbart, E.
Tajkhorshid, E. Villa, C. Chipot, R. D. Skeel, L. Kale and K. Schulten,. 2005, Journal of
Computational Chemistry, Vol. 26, pp. 1781-1802.
3. VMD: Visual molecular. W. Humphrey, A. Dalke and K. Schulten,. 1996, Journal of
molecular graphics,. Vol. 14, pp. 33-38.
4. Particle mesh Ewald: An N. log (N) method for Ewald sums in large systems. Darden T, York
D, Pedersen L,. 1993, the Journal of Chemical Physics, Vol. 98, pp. 10089-10092.

Title of abstract: Transport properties and noise in hydrazine reduced graphene oxide.
Authors: Anindita Sahoo (1), Ryugo Tero (2), Tran Viet Thu (2), Yuji Tanizawa (3), Hiroshi
Okada (2,3), Adarsh Sandhu (2,3), Arindam Ghosh (1)
Affiliation: (1) Department of Physics, Indian Institute of Science, Bangalore 560012, (2)
Electronics Inspired Interdisciplinary Research Institute (EIIRIS), (3) Department of
Electrical and Electronic Engineering, Toyohashi University of Technology, 1-1
Hibarigaoka, Tempaku, Toyohashi 441-8580, JAPAN
Abstract:
Chemically reduced graphene oxide (GO) has attracted immense interest for large scale
production of graphene. This makes electrical properties, in particular resistivity and
flicker noise, in these systems extremely important for variety of electronic applications.
Here we present a study of electrical resistivity, bias stressing and flicker noise (or 1/f
noise) in hydrazine-reduced graphene oxide films as a function of the extent of reduction.
The electrical resistance measurement on individual monolayer flakes of reduced graphene
oxide (RGO) showed that its resistance decreases by four orders of magnitude when
GO is reduced by hydrazine. However, this decrease was associated with an increasing D-
peak in the Raman spectroscopy in comparison to shorter hydrazine treatments indicating
that hydrazine treatment introduces strong localized disorder in RGO, possibly
through crystal defects and impurities. This was further confirmed with bias stressing
and the measurement of 1/f noise (low frequency resistance fluctuation) on the RGO-
FET which showed that the presence of mobile defects in RGO with shorter hydrazine
treatment leads to a faster relaxation of source-drain current and higher value of noise
amplitude. Our experiments indicate that the nature as well as the kinetics of defects
depends on the extent of hydrazine treatment in chemically reduced GO films.

Thermalization threshold in models of 1D fermions
Ranjan Modak ∗ and Subroto Mukerjee
Centre for Condensed Matter Theory, Department of Physics,
Indian Institute of Science, Bangalore
Sriram Ramaswamy
TIFR Centre for Interdisciplinary Sciences, Hyderabad
Abstract
The question of how isolated quantum systems thermalize is an interesting and open one. In
this study we equate thermalization with non-integrability to try to answer this question.
In
particular, we study the effect of system size on the integrability of 1D systems of interacting
fermions on a lattice. We find that for a finite-sized system, a non-zero value of an integrability
breaking parameter is required to make an integrable system appear non-integrable. Using exact
diagonalization and diagnostics such as energy level statistics and the Drude weight, we find that
the threshold value of the integrability breaking parameter scales to zero as a power law with
system size. We find the exponent to be the same for different models with its value depending
on the random matrix ensemble describing the non-integrable system.
We also study a simple
analytical model of a non-integrable system with an integrable limit to better understand how a
power law emerges.
∗ Electronic address: modak@physics.iisc.ernet.in
1

Random matrix theory and gene correlation coefficient statistics
of DNA- Microarray data: Application in understanding the
system biology of gene regulation
Debayan Dey 1 , S. Ramakumar 1
1
Department of Physics, Indian Institute of Science, Bangalore, 560012, India
Abstract: The fundamental question in biology is to understand the mechanism by which a
cell functions. The gene regulation of a cell and its interaction with environment & other cells
makes a complex living organism. Gene regulation is the key process which dictates cell
function and any imbalance in it results in disease. Understanding gene regulation using high
throughput methods is pivotal to understand the holistic nature of gene regulatory network. But it
suffers from large embedded noise within it; so a noise reduction method is very important to
deduce sensible biological information which further can be experimentally tested. DNA-
Microarray technique provides gene expression level data for the whole cell’s activity at a given
time. The understanding of gene correlation matrix provided by the data is essential for
biological elucidation of gene regulatory network.
In our study, we have used Random matrix theory (RMT) to separate non random and system
specific features in the complex biological system from noisy data. We have analyzed various
parameters that affect the threshold determination of Gene correlation network (GCN) e.g. size
of the matrix, no. of variables (biological conditions) used to create the matrix, quality of
microarray data etc. Here, we report the variations in statistical properties of gene correlation
coefficient and its eigenvalue distribution in different biological scenarios. This property reflects
the switching mechanism and dynamicity in the gene regulatory controls. We further discuss on
the gene specific correlation coefficient distribution and its unique properties regarding global
gene regulation. Gene correlations are not constant but change in response to physiological
changes. The variations in the gene correlation and its effect in the gene regulatory network are
analyzed. We have applied this method to understand the gene regulatory network of
Mycobacterium tuberculosis and to understand its global regulatory circuit. We discuss a few
more areas in computational biology where RMT can be used to separate noise from true
correlations.

Violation of Guggenheim Adsorption Rule at Wall-Liquid Interface in Binary
Lennard-Jones Mixture
Shibu Saw 1 , Syed Mohammed Kamil 1 , and Chandan Dasgupta 1,2
1 Centre for Condensed Matter Theory, Department of Physics,
Indian Institute of Science, Bangalore 560012, India
2 Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560 064, India
Guggenheim Adsorption rule states that the majority/minority component enrich the interface
for negative/positive mixing energy of a binary mixture, if surface tension doesn’t play an important
role. We perform molecular dynamics simulation of Binary Lennard-Jones liquid mixtures at the
interface created by a non-preferential wall. We show that the Guggenheim Adsorption rule is obeyed
for the negative mixing energy and violated for positive mixing energy at such interface which is
validated by Density-Functional-Theory using Ramakrishnan-Yussouff functional. We argue that
such violation is due to the dominance of the entropy of the liquid mixture.

Study of effect of alkali mixture on V - O bond length in
Oxyfluoro Vanadate glasses using Raman spectroscopy.
Gajanan V Honnavar # * and K P Ramesh
Department of Physics, Indian Institute of Science, Bangalore – 560 012, India
#
On leave of study from PES Institute of Technology, Bangalore South Campus (Formerly PES
School of Engineering), Near Electronic city, Hosur Road, Bangalore – 560 100, India.
*author for correspondence: gaju@physics.iisc.ernet.in
Abstract:
Raman spectroscopic study on Oxyfluoro Vanadate glasses containing various proportions of lithium
fluoride and rubidium fluoride were carried out to see an effect of mixture of alkali on vanadium -
oxygen (V – O) bond length. Glasses with general formula 40V 2 O 5 - 30BaF 2 - (30 - x) LiF - xRbF (x =
0 – 30) were prepared. Room temperature micro Raman spectra (Fig a and Fig b) of these glass
samples (VBL to VBR) were recorded in back scattering geometry. The data presented is in “reduced
Raman intensity” form with maximum peak scaled to 100[1]. We have used υ = A*exp(BR), where A
and B are fitting parameters (see Franklin D Hardcastle and Israel E Wachs, 1991[2]) to correlate the
bond length R with Raman scattering frequency υ. We observed that variation in bond length and its
distribution about a most probable value can be correlated to the alkali environment present in these
glasses. We also observed that the network forming unit is more homogenous when its first Coordination
is all Rubidium than all Lithium.
References: [1] Wim J Malfait and Werner E Halter, Phy.Rev.B 77, 014201(2008)
[2] Franklin D Hardcastle and Israel E Wachs, J. Phys. Chem. 95, 5031(1999)

Suppression of localization in two dimensionally doped
semiconductors at half-filling
Saquib Shamim 1 , Suddhasatta Mahapatra 2 , Giordano Scapucci 2 , W. M. Klesse 2 , P.B.S.
Mahapatra 1 , Michelle Y. Simmons 2 and Arindam Ghosh 1
1 Department of Physics, Indian Institute of Science, Bangalore 560 012, India
2
Centre for Quantum Computation and Communication Technology, University of New South Wales, Sydney
NSW 2052, Australia
The nature of quantum states, and transport of electrons, in a two dimensional (2D) disordered solid
change significantly in the presence of a background periodic potential, such as that arising from the
host crystal lattice. The interplay of the electron wavelength and lattice periodicity leads to a number
of exotic phenomena, in particular close to half filling, that range from collapse of scaling theory and
Anderson localization, hole-mediated (Nagaoka) ferromagnetism, to new modes of quantum
transport. Much of these phenomena remain unexplored experimentally, primarily due to the lack of a
suitable material platform. Advances in material engineering now allow the dopants, such as
phosphorus (P), confined within one atomic layer inside bulk crystals of silicon (Si) and germanium
(Ge), leading to a unique two-dimensional (2D) electron system whose Fermi energy exists naturally
at or very close to the center of band. Here we demonstrate that quantum interference effect in 2D
Si:P and Ge:P is drastically different from conventional weakly localized 2D electron systems. This
is manifested in two unexpected ways: First, the quantum correction to low temperature conductivity
shows a strong weak antilocalization (WAL), in addition to the conventional weak localization (WL)
behaviour, and second, a spontaneous factor of two suppression in the universal conductance
fluctuations at low areal density of the dopants. We attribute these observations to the emergence of
new modes, called the π-Cooperons and π-Diffusons, of quantum diffusion at half-filled bands, where
electrons propagate through ‘umklapp scattering’ in the presence of a nested of Fermi surface and the
resulting particle-hole symmetry.

Magnetic, Dielectric and Transport Studies of Single Crystal Tb 0.5 Sr 0.5 MnO 3
Hariharan N, Aneesh C, H L Bhat and Suja Elizabeth
Department of Physics, Indian Institute of Science, Bangalore, 560012
ABSTRACT
Half doped Tb 0.5 Sr 0.5 MnO 3 single crystal is grown by four mirror Optical Float-Zone Furnace.
Temperature dependence of dc magnetic susceptibility is carried out in sample with arbitrary
orientation at different fields and a magnetic anomaly is observed around 42 K. Isothermal
magnetization measurements carried at 5 K shows a magnetic hysteresis which is not seen at 50 K, just
above the magnetic anomaly temperature. Dielectric properties are measured in the temperature range
15K-300K with different frequencies ranging from 400Hz to 4MHz .Both real and imaginary parts of the
dielectric constant show clear frequency dispersion which suggests that these materials could be relaxor
ferroelectric. Transport properties of the sample are measured in four probe geometry between 60-
300K. While cooling in this temperature range resistance of the sample steadily increases and was five
orders in magnitude higher at 60 K.
References
1. Appl.Phys.Lett. 96, 152103, (2008).
2. J.Appl.Phys. 83, 7664, (1998).

Direct Numerical Simulation of
Turbulence in the Two-Dimensional
Navier-Stokes-Cahn-Hilliard Equations
Nairita Pal, Anupam Gupta and Rahul Pandit
Department of Physics,
Indian Institute of Science,
Bangalore
November 15, 2012
Abstract
We study a phase-field model for a mixture of two-dimensional(2D)
incompressible fluids, both of which obey the Navier-Stokes Equation.We
elucidate their mixing by introducing a phase-field order parameter
which obeys the Cahn-Hilliard Equation. We have developed
an MPI, parallel, pseudospectral code for the direct numerical simulation
(DNS) of the coupled Navier-Stokes-Cahn-Hilliard Equations in
2D. We present preliminary results from this DNS for decaying turbulence
in this system. We concentrate on statistical properties such as
the energy and dissipation time-series, the enrgy and enstrophy spectra,
dissipation-reduction-type phenomena and the motion of droplets
of the minority phase in this turbulent binary-fluid mixture.
1

Thermoelectric properties of chalcogenide based Cu 2+x ZnSn 1-x Se 4
Ch. Raju a , M. Falmbigl b , P. Rogl b , X. Yan c , E. Bauer c , J. Horky d , M. Zehetbauer d ,
and Ramesh Chandra Mallik a*
a
Department of Physics, Indian Institute of Science, Bangalore 560012, India
b
Institute of Physical Chemistry, University of Vienna, Währingerstrasse 42, A-1090 Wien, Austria
c
Institute of Solid State Physics, TU Vienna, Wiedner Hauptstrasse 8-10, A-1040 Wien, Austria
d
Research Group Physics of Nanostructures Materials, University of Vienna, Boltzmanngasse 5,
Abstract:
A-1090 Wien, Austria
Quaternary chalcogenide compounds Cu 2+x ZnSn 1-x Se 4 (x=0, 0.025, 0.05, 0.75, 0.1, 0.125, 0.15)
were prepared by solid state synthesis. The structural and phase identification of these
compounds were studied by Rietveld X-ray powder diffraction (XPD) refinement combined with
Electron Probe Micro Analyzes (EPMA). The XPD patterns of all samples showed a stannite
phase isotypic with the tetragonal Cu 2 FeSnS 4 -type including ZnSe as a secondary phase. The
samples with the highest Cu-content (x=0.125, 0.15) contained CuSe and SnSe as secondary
phases in addition to ZnSe. Raman spectroscopy was employed for the phase identification in
order to resolve Cu 2 ZnSnSe 4 and ZnSe phase contents, because XPD patterns of both the phases
overlap. In all samples the presence of vibrational modes corresponding to Cu 2 ZnSnSe 4 were
observed and confirm the stannite phase. The electrical resistivity, Seebeck coefficient and
thermal conductivity measurements were carried out as a function of temperature in the range
300-720K. The temperature dependent electrical resistivity data of the undoped sample
confirmed semiconducting behavior in-between 4.2 and 250 K, whereas the samples with
nominal compositions Cu 2+x ZnSn 1-x Se 4 (x=0.05, 0.15) were metallic in nature. The electrical
resistivity is decreasing with increasing doping concentration except for the sample with the
nominal composition Cu 2.1 ZnSn 0.9 Se 4 , probably due to the presence of a high content of the ZnSe
impurity phase. All the samples show a positive Seebeck coefficient throughout the temperature
range investigated, which indicates that the majority carriers are holes. The total thermal
conductivity and phonon thermal conductivity of the undoped sample was significantly less as
compared to the remaining doped samples and this may be due to the larger electronic
contribution and the presence of a higher content of the ZnSe secondary phase in the doped
samples. The maximum figure of merit zT = 0.3 at 720 K occurs for the sample with the nominal
composition Cu 2.05 ZnSn 0.95 Se 4 , but the improvement in zT is rather small due to the presence of
secondary phases. The attempt to improve thermoelectric properties employing a high-pressure
torsion treatment resulted in an enhancement of zT by 30 % up to 625 K for Cu 2.05 ZnSn 0.95 Se 4 .

Thermal Conduction, Feedback and Multiphase Gas in Galaxy
Clusters
Baban Wagh, Prateek Sharma
Galaxy clusters are the largest gravitationally bound, relaxed astronomical objects in the universe, with total
mass around 10 14 − 10 15 M ⊙ , where M ⊙ is a solar mass. Most of the cluster mass, about 85%, is in the dark
matter halo, while 15% is the baryonic mass. Of this 15%, around 90% is in the form of hot, X-ray emitting
plasma (∼ 10 7 − 10 8 K), called the intracluster medium (ICM). Due large gas density in the central regions,
the ICM loses energy primarily by bremsstrahlung radiation, and cools. But there is a discrepancy between
the predicted and the observed cooling rate in galaxy clusters, and this is called the cooling flow problem. It is
believed that the heat lost to cooling is replenished by feedback heating from the central supermassive black hole
and via thermal conduction bringing in heat from larger radii. Sharma and others ([1]) have identified ratio of
the thermal instability timescale and the free-fall time (t TI /t ff ) as an important factor in multiphase formation.
If t TI /t ff 10, then cold gas condenses from the hot phase from the ICM in thermal balance. Condensation
of cold gas is suppressed by thermal conduction, and thermal conduction in dilute ICM plasmas is along the
local magnetic field direction. We study the role of thermal conduction in multiphase gas formation in galaxy
clusters using idealized MHD simulations maintained in global thermal equilibrium. We find that while isotropic
conductivity can effectively suppress cold gas formation, anisotropic thermal conduction does not change the
t TI /t ff criterion based on hydro simulations. We also quantify the relative role of feedback heating and heating
due to thermal conduction in cluster cores.
References
[1] Sharma, P., McCourt, M., Quataert, E., & Parrish, I. J. 2012, MNRAS, 420, 3174
1

Realization of Fermionic Superfluid State in an Optical Lattice
via a Bilaryer Band Insulator
Yogeshwar Prasad, Amal Medhi, Vijay B. Shenoy
Centre for Condensed Matter Theory, Department of Physics,
Indian Institute of Science, Bangalore 560012, India.
Abstract
We propose a model to realize a fermionic superfluid state in an optical lattice, which is one of
the central problems in the area of ultracold quantum gases due to cooling problem. The idea of
our model hinges on a characteristically low entropy state, a band-insulator in an optical bilayer
system and tuning the interaction in such a system to realize the superfluid state. The system is
designed such that the superfluid phase beats other competing phases such as charge density wave
as we show by detailed Monte Carlo calculations. Within the Gaussian approximation, we show
that the superfluid state has a high characteristic temperature scale of the order of hopping energy.
We suggest a route for the possible experimental realization of this state in an optical lattice.
Work supported by CSIR, DAE and DST.
Reference : arXiv:1206.2407v2
1

Superbubble breakout and galactic winds from
disk galaxies
Arpita Roy; Biman B. Nath; Prateek Sharma; Y. Shchekinov
We study the evolution of superbubbles driven by large star clusters
in disk galaxies using Kompaneets approximation and numerical
simulations. We investigate the effect of radiative losses on the
dynamics of superbubbles, in particular the conditions required for
superbubbles to break through the disk material to throw the inner
hot gas into the halo with sufficient speed so as to create a galactic
outow. We nd that our calculations and simulations may explain
the observed threshold star formation surface density required to
create superwinds from disk galaxies.
1

Flow Induced Alignment of water molecules confined inside carbon nanotube: Insight
from MD Simulations
Hemant Kumar, 1, ∗ Prabal K. Maiti, 1, † Chandan Dasgupta, 1, ‡ and A. K. Sood 2, §
1 Centre for Condensed Matter Theory, Indian Institute of Science, Bangalore, India-560012
2 Department of Physics, Indian Institute of Science,Bangalore, India-560012
Molecular dynamics study for the flow induced structural change of water molecules flowing
through carbon nanotubes (CNT) has been presented. We show that dipole moment of the confined
water molecules gets aligned along the axis of nanotube under the effect of flow. With increasing
flow velocities, net dipole moment first increases and eventually saturates to a constant value. This
observation is very similar to Langevin theory of paramagnet where flow velocity acts as an effective
aligning field. Preferential entry of entering water molecules with dipole pointing inward has been
shown to be responsible for this effect. This observation provides a way to control the dipolar
alignment of water inside nano-channel which can be used for various nano-electrical devices and
supports the study by K.Sathya Naryanan and A.K. Sood.
∗
hemant@physics.iisc.ernet.in
† maiti@physics.iisc.ernet.in
‡ cdgupta@physics.iisc.ernet.in
§ sood@physics.iisc.ernet.in

Large linear magnetoresistance in a GaAs/AlGaAs heterostructure
Mohammed Ali Aamir, 1 Srijit Goswami, 1 Matthias Baenninger, 2 Vikram
Tripathi, 3 Michael Pepper, 4 Ian Farrer, 2 David A. Ritchie, 2 and Arindam Ghosh 1
1 Department of Physics, Indian Institute of Science, Bangalore 560 012, India.
2 Cavendish Laboratory, University of Cambridge,
J.J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
3 Department of Theoretical Physics, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
4 Department of Electrical and Electronic Engineering,
University College, London WC1E 7JE, United Kingdom
Large electrical response to magnetic field is one of the key requirements in materials engineering
today. It may seem that a magnetic nature of the material is vital for this [1], but some materials
exhibit it even without magnetism at any scale. Over the last decade, it has been shown that
material inhomogeneity alone can provide a route to large magnetoresistance (MR) in non-magnetic
semiconductors [2, 3]. Interestingly, this MR also has a linear characteristic. Here, we study the MR
of a two-dimensional electron system (2DES) in a GaAs/AlGaAs heterostructure where a disordered
band-structure is induced by applying a large negative gate bias. We find that MR increases linearly
with magnetic field when the device is operated in the non-equilibrium regime with high sourcedrain
bias [4]. Remarkably, the magnitude of MR is as large as 500% per Tesla, thus dwarfing most
non-magnetic materials which exhibit this linearity. Its primary advantage over other materials is
that both linearity and the enormous magnitude are retained over a broad temperature range (0.3 K
to 10 K), thus making it an attractive candidate for on-chip magnetic field sensing.
[1] M. N. Baibich, J. M. Broto, A. Fert, F. N. Van Dau, F. Petroff, P. Etienne, G. Creuzet, A. Friederich, and J. Chazelas,
Phys. Rev. Lett. 61, 2472 (1988).
[2] R. Xu, A. Husmann, T. F. Rosenbaum, M. Saboungi, J. E. Enderby, and P. B. Littlewood, Nature 390, 57 (1997).
[3] M. P. Delmo, S. Yamamoto, S. Kasai, T. Ono, and K. Kobayashi, Nature 457, 1112 (2009).
[4] M. A. Aamir, S. Goswami, M. Baenninger, V. Tripathi, M. Pepper, I. Farrer, D. A. Ritchie, and A. Ghosh, Phys. Rev. B
86, 081203 (2012),

Universal Conductance Fluctuations as a direct probe to valley coherence and
universality class of disordered graphene
Vidya Kochat, Atindra Nath Pal and Arindam Ghosh
Department of Physics, Indian Institute of Science, Bangalore – 560012.
Quantum interference of carriers produces reproducible fluctuations of the order of e 2 /h in the
electrical conductance of mesoscopic semiconductors and metal films as the Fermi energy, magnetic field or
disorder configuration is varied. Both universal conductance fluctuations (UCF) and weak localization (WL)
effects are inevitable components of quantum transport in disordered metals at low temperatures as they
encode crucial information on phase coherence, nature of scattering and symmetry properties of the
Hamiltonian that govern the level statistics of the underlying disordered system. Unlike in conventional metal
films and doped semiconductors where UCF and WL are mainly due to inelastic scattering mechanisms, the
scenario in graphene is more complex due to the existence of two degenerate valleys (K and K’) in its
hexagonal Brillouin zone. The quantum correction to conductivity in graphene is determined by the elastic
scattering mechanisms involving the valleys, namely the inter-valley and intra-valley scattering, in addition to
the phase breaking inelastic scattering events and these competing mechanisms are reflected in the WL and
weak anti-localization of carriers.
Here we present the first unambiguous observation of the effect of valley symmetry on UCF in
monolayer disordered graphene. The UCF magnitude within a single phase coherent box in graphene is
suppressed by an exact factor of four as the carrier density is increased from close to the Dirac point, where
long range Coulomb potential fluctuations dominate, to the high electron or hole density regime, where
potential fluctuations are primarily short range in nature. This also implies a density dependent crossover of
the universality class of graphene from symplectic near the Dirac point to orthogonal at high densities. We also
find that in the presence of a magnetic field, the UCF magnitude decreases by an exact factor of two and this
corresponds to a transition from the symplectic / orthogonal ensemble to the unitary ensemble characterized
by the absence of time reversal symmetry. This work also examines the robustness of time reversal symmetry
in mesoscopic graphene which has been controversial owing to pseudo-magnetic fields arising from ripples,
local moments at edges etc.
The valleys which resemble a spin-like entity can be exploited to form the platform for a new
emerging field termed as valleytronics, having applications ranging from valley-based quantum computation,
to valley filters or polarizers. Our experiments underline a new method using UCF that can probe the valley
coherent states in graphene at low temperatures.
Reference:
Atindra Nath Pal, Vidya Kochat and Arindam Ghosh, Phys. Rev. Lett. 109, 196601 (2012).

Sensory organ like response determines the magnetism of zigzag-edged honeycomb
nanoribbons
Somnath Bhowmick 1 , ∗ Amal Medhi 2 , † and Vijay B Shenoy 2‡
1 Materials Research Center, Indian Institute of Science, Bangalore 560 012, India
2 Centre for Condensed Matter Theory, Department of Physics,
Indian Institute of Science, Bangalore 560 012, India
(Dated: November 12, 2012)
We present an analytical effective theory for the magnetic phase diagram for zigzag edge terminated
honeycomb nanoribbons described by a Hubbard model with an interaction parameter U. We
show that the edge magnetic moment varies as ln U and uncover its dependence on the width W
of the ribbon. The physics of this owes its origin to the sensory organ like response of the nanoribbons,
demonstrating that considerations beyond the usual Stoner-Landau theory are necessary to
understand the magnetism of these systems. A first order magnetic transition from an anti-parallel
orientation of the moments on opposite edges to a parallel orientation occurs upon doping with holes
or electrons. The critical doping for this transition is shown to depend inversely on the width of the
ribbon. Using variational Monte-Carlo calculations, we show that magnetism is robust to fluctuations.
Additionally, we show that the magnetic phase diagram is generic to zigzag edge terminated
nanostructures such as nanodots. Furthermore, we perform first principles modeling to show how
such magnetic transitions can be realized in substituted graphene nanoribbons.
PACS numbers: 75.75.-c, 73.20.-r, 75.70.-i, 73.22.Pr
∗ bsomnath@mrc.iisc.ernet.in
† amedhi@physics.iisc.ernet.in
‡ shenoy@physics.iisc.ernet.in

Evolution of fermionic superfluid across the crossover from three to two dimensions
Sudeep Kumar Ghosh ∗ and Vijay B. Shenoy †
Centre for Condensed Matter Theory, Department of Physics,
Indian Institute of Science, Bangalore 560 012, India
Motivated by recent experiments on the evolution of fermionic superfluid pairing from three to two
dimensions, we construct and study a Bogoliubov-de Gennes theory that accurately accounts for the
periodic potential that induces this dimensional crossover. We consider a system of spin- 1 2 fermions
interacting in the singlet channel via a contact interaction confined by an optical lattice potential
in the z-direction and the motion in plane is free. With the increase in potential depth, the system
gets divided into stacks of two dimensional layers with gradually decreasing inter layer hopping.
The mean field equations are solved numerically to obtain the Bloch bands. For small potential
depth, the linear response of density and pairing gap of the system are obtained numerically and
compared with that of perturbation theory calculations. In deep lattice limit the system becomes
two dimensional and the binding energy is found to be in close agreement with the two dimensional
result. The radio frequency spectrum of the system shows characteristic asymmetric dissociation
peak structure and a clear pairing gap emerges with increasing lattice depth as seen in experiments.
∗ Electronic address: sudeep@physics.iisc.ernet.in
† Electronic address: shenoy@physics.iisc.ernet.in

Title: Induced photoconductivity in large area graphene by electrochemical deposition of thin
films
Authors: Medini Padmanabhan, Uma Maheswari P, Shishir Kumar, Srinivasan Raghavan and
Arindam Ghosh
Abstract: In this work we study the optical response of large area graphene electrochemically
integrated with light-sensitive semiconductors. Chemical vapor deposited (CVD) graphene is
transferred onto a suitable substrate such as glass or silicon wafer. Two- point resistance of
graphene is measured with and without a layer of electrodeposited CdS. We find that, in the
presence of CdS, appreciable photoconductivity is induced in graphene. The hybrid-device is
observed to respond to light at a much faster timescale compared to the characteristic
photodesorption curves of bare graphene. We explore various avenues of integrating this growth
technique with solar cell architectures.

Microwave assisted synthesis of single crystalline ternary alloy-Bi 2-x Sb x Te 3
for thermoelectric applications
Mitali Banerjee 1 , R.Venkatesh 2 , Arindam Ghosh 1 and N. Ravishankar 2
1 Department of physics Indian Institute of Science,Bangalore 560012, India,
2 Materials Research Centre, Indian Institute of Science,Bangalore 560012, India
ABSTRACT
The discovery of colossal enhancement of thermoelectric figure of merit in bismuthbased
chalcogenide nanostructures has identified them as potential candidates for
thermoelectric applications. Especially one shot facile synthesis of p-type bismuth antimony
telluride which has been reported to show a large thermoelectric power around the room
temperature still remains as a challenge. We report a surfactant-assisted wet chemical
synthesis of nanostructures of single crystalline ternary Bi 2-x Sb x Te 3 (0.5

Sharp Raman anomalies and broken adiabaticity at a pressure induced
transition from band to topological insulator in Sb 2 Se 3
Achintya Bera 1 , Koushik Pal 2, 3 , D. V. S. Muthu 1 , Somaditya Sen 4 , Prasenjit Guptasarma 4 ,
U. V. Waghmare 3 , and A. K. Sood 1
1 Department of Physics, Indian Institute of Science, Bangalore-560012, India
2 Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific
Research, Bangalore-560064, India
3 Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research,
Bangalore-560064, India and
4 Department of Physics, University of Wisconsin-Milwaukee, Wisconsin-53211, USA
Recently discovered three-dimensional Topological insulators (TI) have attracted a lot of
attention of researchers from diverse backgrounds due to robust and exotic phenomena, such
as quantum spin Hall states, arise from the geometric and topological properties of the
manifold of their electronic states. However, experimental evidence for nontrivial topology of
electronic states is so far mainly based on the time-reversal symmetry protected chiral surface
states. Signatures of the nontrivial topology of a TI in its bulk behaviour are subtle, and not
yet identified. Our work presented here establishes that (a) bulk signatures of the electronic
topology become significant and detectable as anomalies in the phonon frequency and
linewidth of E g Raman mode at an electronic topological transition (specifically in single
crystal Sb 2 Se 3 ), (b) their origin lies in physical mechanisms that involve going beyond
adiabatic approximation as a metallic (vanishing gap) state of the bulk appears at the
transition, and (c) they involve electron-phonon couplings some of which are not captured by
the standard methods to calculate electronic structure.
References:
[1] Zhang, H. et al. “Topological insulators in Bi 2 Se 3 , Bi 2 Te 3 and Sb 2 Te 3 with a single Dirac
cone on the surface”. Nature Phys. 5, 438-442 (2009).
[2] G.K. Pradhan et al. “Raman signatures of pressure induced electronic topological and
structural transitions in Bi 2 Te 3 ”. Solid State Commun. 152, 284–287 (2012)

Using cis peptide containing fragments for functional annotation
of proteins
Sreetama Das 1 , Suryanarayanarao Ramakumar 1 and Debnath Pal 2
1 Department of Physics, 2 Supercomputer Education Research Centre, Indian Institute of
Science, Bangalore 560012, India
BACKGROUND: Proteins are linear polymers of the twenty naturally occurring amino
acids, and are essential for many cellular processes. The consecutive amino acids are
covalently linked by a peptide bond, which may be in cis or trans conformation. There are a
large number of proteins whose structures are known but their functions are not. Here from
arises the need for protein function prediction methods.
Cis peptide bonds, and especially those involving non-Proline amino acids, although rare in
occurrence in protein structures, are implicated to play an important role in their structure
and/ or function. It is, therefore, pertinent to ask if singular protein segments containing cis
peptides can provide functional annotation of proteins with known structure but unknown
function.
RESULTS:
We used our own protein backbone geometry-based clustering algorithm to group cis peptide
containing fragments of specific lengths. Of these we identified fragments of length 6 ─ 8,
suitable for annotation studies. Grouped fragments of these lengths were subjected to analysis
of enrichment of Gene Ontology (GO) molecular function terms. Fragments associated with
statistically-enriched GO terms were identified as functionally important. These functionally
“significant” fragments were thereafter searched in homologous proteins. Their utility as
singular cis-containing peptide fragment for providing functional annotation was thereafter
confirmed through a high area under the Receiver-Operator-Curve (ROC). Subsequently, we
are attempting to locate these fragments in proteins of unknown function for annotation
purposes.
CONCLUSIONS:
Fragments associated with enriched GO molecular function showing propensities ≥ 20 and p-
value thresholds ≤ 0.05 point to cis peptide-containing fragments important for protein
function. This fact was verified through a literature survey. When used for identifying similar
fragments in a set of non-redundant entries from the PDB database, the fragments alone were
sufficient to identify close homologues and related proteins. Currently, we are establishing
the utility of these fragments for functionally annotating proteins with no known function.

Study of Phonon anharmonic effects in pyrochlores
P K Verma ∗ , U V Waghmare † , A K Sood ‡ , H R Krishnamurthy §
Deparment of Physics, Indian Institute of Science, Bangalore, India
Jawaharlal Nehru Center for Advanced Scientific Research, Bangalore, India
Structural and electronic properties of ideal pyrochlores with the composition Y 2 B 2 O 7
(where B = Ti, Zr, and Ir) were studied using the first-principles calculations. Both Y 2 Ti 2 O 7
and Y 2 Zr 2 O 7 are insulators while Y 2 Ir 2 O 7 is metal. A large anomalous Born effective charge
was observed for Ti, attributing to the hybridization between the occupied 2p states of the
oxygen and unoccupied d states of the B cation. Density functional perturbation theory
calculations were performed to obtain the phonon properties. While all the phonon frequencies
of Y 2 Zr 2 O 7 and Y 2 Ir 2 O 7 were found to be real valued as one would expect, Y 2 Ti 2 O 7
showed instabilities with respect to some optical distortions, in that 6 of the frequencies
were found to be imaginary. This is likely to underlie the anomalous temperature dependent
of the phonons that have been seen in other titanate pyrochlores. In a study as to how to
stabilize Y 2 Ti 2 O 7 , we found that the system becomes stable at 7GPa at the Γ point, but
remains unstable at other k-points in the Brillouin Zone; it becomes stable at all k-points
at 12GPa. Small distortions of the atomic positions inside the unit cell can also stabilize
the structure at ambient pressure. Phonon-phonon anharmonic effects are very important in
titanate pyrochlores as have been experimentally seen in other titanates. We have treated
the effects of these upto third order anharmonic corrections. We found phonon anomalies
for some of the phonon modes of Y 2 Ti 2 O 7 , in qualitative agreement with experiments.
∗
†
‡
§
Electronin address: pramod@physics.iisc.ernet.in
Electronin address: waghmare@jncasr.ac.in
Electronin address: asood@physics.iisc.ernet.in
Electronin address: hrkrish@physics.iisc.ernet.in

Optoelectronic properties of graphene-MoS 2 hybrids
Kallol Roy, 1 Medini Padmanabhan, 1 Srijit Goswami, 1 T. Phanindra Sai, 1
Gopalakrishnan Ramalingam, 2 Srinivasan Raghavan, 2 and Arindam Ghosh 1
1 Department of Physics, Indian Institute of Science, Bangalore 560012, India and
2 Materials Research Center, Indian Institute of Science, Bangalore 560012, India
Abstract
Graphene is a very interesting layered material because of its high quality electronic characteristics
which can be tuned by application of a gate voltage. However optical absorption property of
single layer graphene is very poor, and hence most of the light (> 95%) gets transmitted. Molybdenum
disulphide (MoS 2 ) is another layered material which is optically active and its bandgap
changes with number of layers. In this report we have shown that the hybrid structure of graphene
and MoS 2 can be made to integrate their electronic and optical characteristics, and gate tunable
optical response can be induced in graphene.

Bio – sensors based on electrical and optical properties of
Carbon nanotubes & Graphene oxide
K. S. Vasu a , S. Sridevi b , S. Asokan b , N. Jayaraman c and A. K. Sood a
a Department of Physics, Indian Institute of Science, Bangalore
b Department of Instrumentation and Applied Physics, Indian Institute of Science, Bangalore
c Department of Organic Chemistry, Indian Institute of Science, Bangalore.
We show that single walled carbon nanotubes (SWNTs) decorated with sugar functionalized
poly (propyl ether imine) (PETIM) dendrimer (DM) is a very sensitive platform to quantitatively
detect carbohydrate recognizing proteins, namely, lectins. The mannose attached PETIM
dendrimers undergo charge – transfer interactions with the SWNT. The changes in the
conductance of the dendritic sugar functionalized SWNT after addition of lectins in varying
concentrations were found to follow the Langmuir type isotherm, giving the concanavalin A
(Con A) – mannose affinity constant to be 8.5 x 10 6 M -1 [1].
We have recently shown that etched Fiber Bragg Gratings (eFBGs) coated with nano – carbon
materials can be used as potential biochemical sensors. The shift in the Bragg wavelength (∆λ B )
with respect to the λ B values of SWNT (or GO) – DM coated eFBG for various concentrations of
lectin follows Langmuir type adsorption isotherm and quantitatively analyzed to establish the
detection limit [2].
References:
1) K. S. Vasu, K. Naresh, R. S. Bagul, N. Jayaraman and A. K. Sood, Appl. Phys. Lett. 101,
053701 (2012).
2) S. Sridevi, K.S. Vasu, N. Jayaraman, S. Asokan and A.K. Sood (2013).

Violation of Chandrasekhar mass limit: Strongly
magnetized white dwarfs as progenitors of
super-Chandrasekhar type Ia supernovae
Upasana Das, Banibrata Mukhopadhyay
Department of Physics, Indian Institute of Science, Bangalore 560012, India
upasana@physics.iisc.ernet.in, bm@physics.iisc.ernet.in
November 15, 2012
Abstract
Recent observations of peculiar Type Ia supernovae - SN 2006gz, SN 2007if,
SN 2009dc, SN 2003fg - seem to suggest super-Chandrasekhar-mass white dwarfs
with masses up to 2.4 - 2.8 solar mass, as their most likely progenitors. We show
that strongly magnetized white dwarfs can violate the Chandrasekhar mass limit
(which is 1.44 solar mass) significantly, owing to the Landau quantization of the
relativistic electron degenerate gas. Interestingly, our results seem to lie within
the above observational limits. We also establish that accretion on to commonly
observed magnetized white dwarfs, coupled with the phenomenon of flux freezing,
leads to the generation of very strong magnetic fields in the interiors of these white
dwarfs. This would in turn explain the super-Chandrasekhar masses according to
our proposed theory.
1

Superfluidity in Bricks!
Arijit Haldar and Vijay B. Shenoy
Centre for Condensed Matter Theory
Indian Institute of Science, Bangalore 560 012
An optical brick lattice has recently be realized by the ETH group. We show
that this systems offers the possibility of realizing a superfluid state of fermions with a
high transition temperature. The brick lattice defined by three hopping parameters, in
a regime, has a band gap. Exploiting this, we propose to the band insulator obtained
in this regime to beat the entropy problem, to obtain an optical lattice superfluid by
tuning an attractive interaction between the fermions. By studying the quantum field
theory of the system including Gaussian fluctuations, we estimate the Kosterlitz-
Thouless transition temperature of the system. We find that in a regime of parameters
the transition temperature is “ high” , i.e., of the order of the hopping scale.
See also: Related poster by Yogeshwar Prasad et al.