nanoelectronics - Institut d'Études Scientifiques de Cargèse (IESC)

2012
22 Octobre
27 Octobre
WORKSHOP
« NANOELECTRONICS:
CONCEPTS,
THERORY AND MODELLING »
Jean‐Louis PICHARD
IRAMIS / SPEC
CEA ‐ Saclay
91191 Gif sur Yvette
0169087236
jean‐louis.pichard@cea.frz
Direction scientifique :
Giovanna Chimini
Contact :
Dominique Donzella
tél : 04 95 26 80 40
www.iesc.univ-corse.fr

Nanoelectronics:
Concepts, Theory and Modeling
Network meeting
and
workshop on
thermoelectric transport
Program and Abstracts
21-27 October 2012
Cargèse, Corsica

Afternoon
Morning
Timetable
Monday Tuesday Wednesday Thursday Friday
09:00 Pichard
09:15 Benenti
09:55 Imry
11:00 Coffee
11:30 Saito
09:00 Beenakker
09:45 Molenkamp
10:50 Coffee
11:20 Narayan
12:05 Fleury
08:45 Georges
09:50 Benenti
10:30 Coffee
11:00 Volz
11:40 Round
Table
09:00 Heiblum
10:05 Dolcetto
10:25 Coffee
10:55 Kotetes
11:25 Diez
11:55 Pikulin
09:00 Edge
09:30 Tworzydlo
10:00 Chakraborty
10:15 Coffee
10:45 Raimondi
11:15 Ochoa
11:30 Weick
12:00 Peterfalvi
14:30 Pekola
15:35 Schön
16:15 Coffee
16:40 Bourgeois
17:20 Moskalets
14:30 R Sánchez
15:10 D Sánchez
15:50 Coffee
16:20 Sothmann
16:50 Sols
17:20 Lambert
Excursion
14:30 Rakyta
15:00 Ferrer
15:30 Coffee
16:00 Poster
presentations
16:30 Posters
14:30 Gorini
15:00 Kleshchonok
15:30 Ferradas
15:45 Coffee
16:15 Gómez León
16:30 García Suárez
16:45 Evangelou

Program
Monday October 22
09h00 – 09h15 Jean-Louis Pichard: Welcome, Program of the week, Miscellaneous
09h15 – 09h55 Giuliano Benenti: Introduction to a few basic concepts in thermoelectric transport
09h55 – 11h 00 Yoseph Imry: Thermal Transport and Thermoelectric Coefficients Near the
Anderson Transition and in 3-Terminal Molecular-Type Junctions
11h00 – 11h 30 Coffee break
11h30 – 12h25 Keiji Saito: Exact solution of a Levy walk model for anomalous heat transport
12h30 Lunch
14h30 – 15h35 Jukka Pekola: Experiments on the distribution of dissipation in electron tunneling
15h35 – 16h15 Gerd Schön: Single-Electron Tunneling and the Fluctuation Theorem
16h15 – 16h40 Coffee break
16h40 – 17h20 Olivier Bourgeois: Impact of nanophononics on thermoelectricity: measurements and
methods
17h20 – 18h00 Michael Moskalets: Scattering approach to heat transport. Application to a singleelectron
emitter for chiral wave-guides
__________________________________________________________________________
Tuesday October 23
09h00 – 09h45 Carlo Beenakker: Random-matrix theory of thermoelectricity
09h45 – 10h50 Laurens Molenkamp: Thermoelectric Properties of Semiconductor Nanostructures
10h50 – 11h 20 Coffee break
11h20 – 12h05 Vijay Narayan: Anomalous Thermopower in a Low-Density Two-Dimensional Electron
System: Metallic Dependence, Giant Magnitude and Oscillatory density-dependence
12h05 – 12h25 Geneviève Fleury: Delay Time and Thermopower Distributions at the spectrum edges
of a chaotic scatterer
12h30 Lunch
14h30 – 15h10 Rafael Sánchez: Harvesting fluctuations at electrical hot spots
15h10 – 15h50 David Sánchez: Scattering theory of nonlinear thermoelectric transport

15h50 – 16h20 Coffee Break
16h20 – 16h50 Björn Sothmann: Magnon-driven quantum-dot heat engine
16h50 – 17h20 Fernando Sols: Electron refrigeration by nonadiabatic pumping and related questions
on quantum cooling
17h20 – 17h50 Colin Lambert: Giant Thermopower and Figure of Merit in Single-Molecule Junctions
__________________________________________________________________________
Wednesday October 24
08h45 – 09h50 Antoine Georges: Thermoelectric properties of strongly correlated quantum systems
09h50 – 10h30 Giuliano Benenti: Thermopower and thermoelectric efficiency in systems with
broken time-reversal symmetry
10h30 – 11h00 Coffee break
11h00 – 11h40 Sebastian Volz: Heat and Nanotechnologies : Focus on Thermoelectricity
11h40 – 12h40 Round Table: Thermoelectric energy conversion, insights, prospects for real
applications?
12h45 Lunch
Excursion and Dinner
__________________________________________________________________________
Thursday October 25
09h00 – 10h05 Moty Heiblum: Observation of neutral modes in the fractional quantum Hall regime
10h05 – 10h25 Giacomo Dolcetto: Tunneling between helical edge states through extended contacts
10h25 – 10h55 Coffee break
10h55 – 11h25 Panagiotis Kotetes: Spinful Majorana fermions and magnetoelectricity in junctions of
1D quantum wire-superconductor heterostructures
11h25 – 11h55 Mathias Diez: Andreev reflection from a topological superconductor with chiral
symmetry
11h55 – 12h15 Dmitry Pikulin: Zero-bias conductance peak from weak antilocalization in a Majorana
nanowire
12h30 Lunch
14h30 – 15h00 Peter Rakyta: Electronic standing waves on the surface of the topological insulator
Bi 2 Te 3

15h00 – 15h30 Jaime Ferrer: How does Exact DFT compares with exact solutions in simple models of
strongly correlated electrons?
15h30 – 16h00 Coffee break
16h00 – 16h30 Poster Presentations
16h30 – 18h00 Posters
__________________________________________________________________________
Friday October 26
09h00 – 09h30 Jonathan Edge: Metallic phase of the quantum Hall effect in four-dimensional space
09h30 – 10h00 Jakub Tworzydlo: Thermal metal in topological superconductors.
10h00 – 10h15 Akash Chakraborty : Nanoscale inhomogeneities in diluted magnetic systems : Effects
on Curie temperature and spontaneous magnetization
10h15 – 10h45 Coffee break
10h45 – 11h15 Roberto Raimondi: Onsager relations in a two-dimensional electron gas with spinorbit
coupling
11h15 – 11h30 Héctor Ochoa: Spin-orbit coupling assisted by flexural phonons in graphene
11h30 – 12h00 Guillaume Weick: Massless Dirac bosons in honeycomb plasmonic lattices
12h00 – 12h30 Csaba Peterfalvi: Electron Focussing in Graphene
12h30 Lunch
14h30 – 15h00 Cosimo Gorini: Theory of scanning gate microscopy
15h00 – 15h30 Andrii Kleshchonok: Electron interferometry with a Quantum Point Contact: Effect of
electron-electron interaction and temperature
15h30 – 15h45 Rubén Ferradas: Symmetry-induced interference effects in metalloporphyrins wires
15h45 – 16h15 Coffee break
16h15 – 16h30 Álvaro Gómez León: Ac magnetic fields coupled to spin qubits
16h30 – 16h45 Víctor García Suárez: Nonequilibrium transport response from equilibrium transport
theory
16h45 – 17h15 Spiros Evangelou: Quantum chaos in disordered graphene

Monday
Abstracts
Monday, October 22
Introduction to a few basic concepts in thermoelectricity
Giuliano Benenti
Center for Nonlinear and Complex Systems, Università degli Studi dell'Insubria, Via Valleggio
11, 22100 Como, Italy
I will review fundamental aspects of heat to work conversion, including the phenomenological
coupled charge and heat transport equations of non-equilibrium thermodynamics, the
Onsager reciprocity relations, the figure of merit ZT for thermoelectric efficiency, the
Curzhon-Ahlborn efficiency at maximum power, the Wiedemann-Franz law and Mott's
formula.
__________________________________________________________________________
Thermal Transport and Thermoelectric Coefficients Near the Anderson Transition and
in 3-Terminal Molecular-Type Junctions (*)
Yoseph Imry
Weizmann Institute of Science
(*) Patent application pending
We start by reviewing thermal and thermoelectric linear transport, including the various
coefficients the symmetry relations among them (Onsager) and what determines their
magnitudes. Applications will be briefly mentioned along with the requirements on the above
coefficients.
Next, the Anderson localization transition will be considered at finite temperatures. This
includes the electrical conductivity as well as the electronic thermal conductivity and the
thermoelectric coefficients [1-3]. The latter becomes relatively large at low temperatures near
the transition, its interesting critical behavior is found. A method for characterizing the
conductivity critical exponent, an important signature of the transition, using both the
conductivity and thermopower measurements, is outlined.
Then, the thermoelectric transport through a molecular bridge (or a corresponding quantumdot
arrangement) - a model nanosystem - will be discussed, with an emphasis on the effects
of inelastic processes of the transport electrons caused by the coupling to the vibrational
modes of the molecule. In particular it is found that when the molecule is coupled to a
thermal bath of its own, which may be at a temperature different from those of the electronic
reservoirs, a heat current between the molecule and the reservoir can be generated by the
usual electric current. Expressions for the transport coefficients governing this conversion
and similar ones are derived, and possible scenarios for increasing their magnitudes are
outlined along with related semiconductor junction systems [4].
The latter interesting case of three terminals with two types of carriers presents novel
possibilities. We shall conclude by demonstrating its advantage over usual two-terminal
situations, for thermoelectric energy conversion [5].
[1] M. Cutler and N. F. Mott, Phys Rev. 181, 1336 (1969)

Monday
[2] U. Sivan and Y. Imry, Phys Rev B33, 551 (1986)
[3] Y. Imry and A. Amir, The localization transition at finite temperatures: electric and thermal
transport, in 50 years of Anderson Localization, edited by E. Abrahams (World Scientific,
Singapore, 2010) in press, arXiv:1004.0966
[4] O. Entin-Wohlman, Y. Imry and A. Aharony, Three-terminal thermoelectric transport
through a molecular junction, Phys. Rev. B 82, 115314 (2010); R.Sanchez and M.Büttiker,
ibid. 83, 085428 (2011); J-H Jiang, O. Entin-Wohlman and Y. Imry, Phys Rev B 85, 075412
(2012), and to be published.
[5] J-H Jiang, O. Entin-Wohlman and Y. Imry, in preparation
__________________________________________________________________________
Exact solution of a Levy walk model for anomalous heat transport
Keiji Saito
Physics Department, Keio University
Based on results obtained from a large number of numerical simulations and various
analytical approaches it is now believed that Fourier's law is not valid in one and two
dimensional mechanical systems (in particular models where momentum is conserved) and
heat conduction is anomalous. Anomalous behavior in heat conduction is not only a
theoretical issue but recently of experimental relevance in several low-dimensional material
such as carbon-nanotube, and Graphene. Indicators of the anomaly include | (i) in steady
states the dependence of the heat current J on system size L shows the scaling behavior , (ii)
the temperature profiles across systems in nonequilibrium steady states are found to be
nonlinear even for very small applied temperature diferences and, (iii) the spreading of heat
pulses in anharmonic chains is superdiusive. The Levy-walk model is known to provide a
good description of anomalous heat conduction in one-dimensional systems. In this model
the heat carriers execute Levy-walks instead of normal diffusion as expected in systems
where Fourier's law holds. Here we calculate exactly the average heat current, the large
deviation function of its fluctuations and the temperature profile of the Levy-walk model
maintained in a steady state by contact with two heat baths (the open geometry) [1]. We find
that the current is nonlocally connected to the temperature gradient. As observed in recent
simulations of mechanical models, all the cumulants of the current fluctuations have the
same system-size dependence in the open geometry. The case of the ring geometry is also
discussed.
[1] Abhishek Dhar, Keiji Saito and Bernard Derrida, arXiv:1207.1184
__________________________________________________________________________
Experiments on the distribution of dissipation in electron tunneling
Jukka Pekola
Aalto University, Helsinki, Finland
I discuss work, heat and fluctuation relations in single-electron tunneling driven by a gate
voltage. Our experiments confirm the validity of the most common fluctuation relations under
isothermal conditions. I discuss a feed back mechanism by which information can be
converted into energy stored in a capacitor in a single-electron circuit. Finally I propose a
measurement of work in a quantum system using a calorimetric detection.

Monday
Single-Electron Tunneling and the Fluctuation Theorem
Gerd Schön 1 , Y. Utsumi 2 , D. S. Golubev 1 , M. Marthaler 1
1
Institut für Theoretische Festkörperphysik, Karlsruhe Institute of Technology, 76128
Karlsruhe, Germany
2
Department of Physics Engineering, Faculty of Engineering, Mie University, Tsu, Mi-e, 514-
8507, Japan
Experiments on the direction-resolved full-counting statistics of single-electron tunneling
allow testing the fundamentally important Fluctuation Theorem (FT). At the same time, the
FT provides a frame for analyzing such data.
Here we consider tunneling through a double quantum dot (DQD) system which is coupled
capacitively to a quantum point contact (QPC) detector. Fluctuations of the environment,
including the shot noise of the QPC, lead to an enhancement of the effective temperature in
the FT. We provide a quantitative explanation of this effect [1].
In addition we discuss the influence of the finite detector bandwidth on the measurements.
Furthermore, we derive the full counting statistics for the coupled DQD - QPC system and
obtain the joint probability distribution of the charges transferred through the DQD and the
QPC, which is consistent with the fluctuation theorem (FT) [2]. The system can be described
by a master equation with tunneling rates depending of the counting fields and satisfying a
generalized local detailed-balance relation.
[1] Bidirectional Single-Electron Counting and the Fluctuation Theorem, Y. Utsumi, D.S.
Golubev, M. Marthaler, K. Saito, T. Fujisawa, and G. Schön, Phys. Rev. B 81, 125331 (2010)
[2] Fluctuation theorem for a double quantum dot coupled to a point-contact electrometer,
D.S. Golubev, Y. Utsumi, M. Marthaler, G. Schön, Phys. Rev. B 84, 075323 (2011)
__________________________________________________________________________
Impact of nanophononics on thermoelectricity: measurements and methods
Olivier Bourgeois, Christophe Blanc, Hossein Ftouni, Dimitri Taïnoff
Institut Néel, Université Joseph Fourier-CNRS, 25 rue des Martyrs, BP 166, 38042 Grenoble
Cedex 9, France
We will review recent progresses made in nanophononics to get a better approach in energy
harvesting [1,2]. The manipulation of phonons in low dimensional suspended structures
opens up very important questions especially at low temperature [3,4]. Different concepts
have been proposed to transform single crystalline materials into phonon glasses: phononic
crystals, suspended structured membranes, nanoengineered materials. The possible
reduction of phonon transport in these structures by opening a gap in the dispersion relation,
by reducing the group velocities or by decreasing the phonon mean free path is a possible
path towards better thermoelectrics.
The measurement of very small suspended systems requires the development of highly
sensitive experimental techniques. We will describe state of the art experimental methods
that have been proposed for the measurement of tiny energy exchange from room
temperature to very low temperature [5] (thermal conductance measurement and heat
exchange in general). We will show recent experiments that play with phonons at the
nanoscale. To conclude we will see that nanophononics at low temperature is still a very
open subject especially with suspended systems containing electrons like graphene or two
dimensional electron gas.

Monday
[1] Clivia M Sotomayor Torres and Jouni Ahopelto, Position Paper on Nanophotonics and
Nanophononics, E-Nano Newsletter (Issue 24) Publishing Date: 2011-12-31.
[2] J. Tang et al. Holey Silicon as an Efficient Thermoelectric Material, Nano Letters 10, 4279
(2010)
[3] J-S. Heron, C. Bera, T. Fournier, N. Mingo, and O. Bourgeois, Blocking phonons via
nanoscale geometrical design, Phys. Rev. B 82, 155458 (2010).
[4] Christophe Blanc, Ali Rajabpour, Sebastian Volz, Thierry Fournier, and Olivier Bourgeois
Phonon Glass Behaviour in Corrugated Silicon Nanowires Due to Phonon Backscattering.
(2012)
[5] A. Sikora, H. Ftouni, J. Richard, C. Hébert, D. Eon, F. Omnès, and O. Bourgeois, Highly
sensitive thermal conductivity measurements of suspended membranes (SiN and diamond)
using a 3ω-Völklein method. Rev. Sci. Instrum. 83, 054902 (2012).
__________________________________________________________________________
Scattering approach to heat transport. Application to a single-electron emitter for
chiral wave-guides
Michael Moskalets
Department of Metal and Semiconductor Physics, National Technical University “Kharkiv
Polytechnical Institute” 61002 Kharkiv, Ukraine
We present a scattering matrix approach to heat transport in dynamical mesoscopic
structures for non-interacting electrons [1-3]. We show quite generally existence of two
effects, heat generation and heat pumping. In particular we analyze energetics [4] of a
single-particle source emitting on-demand electrons and holes [5]. It turns out that the energy
of emitted particles is not fixed unlike their charge. Therefore, even a regular particle flow
carries a fluctuating heat. These heat fluctuations can be measured as temperature
fluctuations of an attached thermometer, which in turn can be measured as the fourth
cumulant of a potential if a thermometer serves simultaneously as a voltage probe. Notice
the fluctuations of a heat of a regular particle flow are a feature of an essentially dynamical
source and it is absent for a DC source. We analyze a heat production [4] of two subsequent
single-particle sources working as a tunable two-particle source [6]. We show that unlike a
charge current the heat current can be non-additive. In particular, in the adiabatic regime the
heat production can be suppressed if the second source is tuned to emit a hole at the time
when the first source emits an electron or vice versa. We show also that the heat generated
becomes enhanced if two electrons or two holes are emitted simultaneously.
[1] M. Moskalets, M. Büttiker, Floquet scattering theory of quantum pumps, Phys. Rev. B 66,
205320 (2002)
[2] L. Arrachea, M. Moskalets, Energy transport and heat production in quantum engines, in
Handbook of Nanophysics: Nanomedicine and Nanorobotics, ed. by Klaus D. Sattler (CRC
Press, Taylor & Francis Group), 38-1 (2010)
[3] M. Moskalets, Scattering matrix approach to non-stationary quantum transport, (Imperial
College Press, London), 280 p. (2011)
[4] M. Moskalets, M. Büttiker, Heat production and current noise for single- and double-cavity
quantum capacitors, Phys. Rev. B 80 081302 (2009)
[5] G. Fève, A. Mahé, J.-M. Berroir, T. Kontos, B. Plaçais, D. C. Glattli, A. Cavanna, B.
Etienne, Y. Jin, An On-Demand Coherent Single-Electron Source, Science 316, 1169 (2007)
[6] J. Splettstoesser, S. Ol’khovskaya, M. Moskalets, M. Büttiker, Electron counting with a
two-particle emitter, Phys. Rev. B 78, 205110 (2008)

Tuesday
Tuesday, October 23
Random-matrix theory of thermoelectricity
Carlo Beenakker
Instituut-Lorentz, Leiden University, P.O. Box 9506, 2300 RA Leiden, The Netherlands
Since Landauer, Büttiker, and Imry’s work in the 1980’s we know that the study of electrical
conductance in mesocopic systems is related to the study of the statistical properties of
scattering matrices. Random-matrix theory was developed as a powerful tool to make
universal predictions, independent of microscopic details of the system. Thermoelectric
transport properties typically involve energy derivatives of the conductance, and one might
wonder whether random-matrix theory can play an instructive role as well. The relevant
matrix is the socalled time-delay matrix, which contains dynamical information on the
electron scattering. We review some older work on the random-matrix theory of
thermoelectricity, and also some recent work on thermal conduction in topological
superconductors.
General background material: ArXiv:0904.1432
__________________________________________________________________________
Thermoelectric Properties of Semiconductor Nanostructures
Laurens W. Molenkamp
Physikalisches Institut (EP3) der Universität Würzburg, Am Hubland, 97074 Würzburg
Thermoelectric experiments on nanostructures are often complicated by the need to apply a
temperature difference of a few K across a device a few 100 nm in size. In semiconductors,
such large gradients lead to very strong phonon drag effects, that overwhelm the electronic
thermoelectric effects a transport physicist usually is interested in.
Over the years, we have developed a current heating technique that utilizes the relatively
small electron-acoustic phonon coupling in semiconductors to create a thermal gradient in
the electronic system only. This has allowed us to study in detail the thermoelectric
properties of quantum point contacts and quantum dots. More recently, we have started to
apply the technique to spintronic nanostructures. In this talk, I will present some of our recent
results in this direction, with examples such as the thermoelectric properties of a dot in the
Kondo regime, thermal rectification and the diffusion thermopower of (Ga,Mn)As.

Tuesday
Anomalous Thermopower in a Low-Density Two-Dimensional Electron System:
Metallic Dependence, Giant Magnitude and Oscillatory density-dependence
Vijay Narayan 1 , M. Pepper 2 , J. Griffiths 1 , H. Beere 1 , F. Sfigakis 1 , G. Jones 1 , D. Ritchie 1 and
A. Ghosh 3
1 Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3
0HE, United Kingdom
2 Department of Electronic and Electrical Engineering, University College London, Torrington
Place, London WC1E 7JE, United Kingdom
3 Department of Physics, Indian Institute of Science, Bangalore 560012, India
We present thermopower S and electrical resistivity ρ 2DES measurements in a low-density
(~ 10 14 m -2 ) two-dimensional electron system (2DES). We are interested in the regime where
ρ 2DES >> h/e 2 and consequently the 2DES is expected to be strongly localised. Remarkably,
however, we observe several aspects to the 2DES behaviour that are not consistent with
insulating behaviour. First, the temperature-dependence of S is manifestly metallic, S
growing linearly as a function of temperature up to ≈ 0.7 K. Second, the magnitude of S
exceeds the Mott value valid for non-interacting metallic 2DESs at similar carrier densities by
over two orders of magnitude. And third, we observe a seeming decoupling between ρ 2DES
and S in their density-dependence whereby strong oscillations and even sign changes are
observed in the latter which are completely absent in the former. We explore the role of the
many-body Coulomb potential in these observations and the scope offered by this system
towards sub-Kelvin Peltier refrigeration.
[1] Vijay Narayan, M. Pepper, J. Griffiths, H. Beere, F. Sfigakis, G. Jones, D. Ritchie and
A. Ghosh, Unconventional metallicity and giant thermopower in a strongly interacting twodimensional
electron system, Phys. Rev. B 86, 125406 (2012)
[2] Vijay Narayan, M. Pepper, J. Griffiths, H. Beere, F. Sfigakis, G. Jones, D. Ritchie and
A. Ghosh, Evidence of Novel Quasiparticles in a Strongly Interacting Two-Dimensional
Electron System: Giant Thermopower and Metallic Behaviour, J. Low Temp. Phys
(accepted), DOI 10.1007/s10909-012-0718-0
__________________________________________________________________________
Delay-time and thermopower distributions at the spectrum edges of a chaotic
scatterer
A. Abbout (1,2) , G. Fleury (1) , J.-L. Pichard (1) and K. Muttalib (3)
(1)
Service de Physique de l'Etat Condensé CNRS URA 2464, CEA Saclay, 91191 Gif-sur-
Yvette, France
(2)
Laboratoire CRISMAT, CNRS UMR 6508, 6 boulevard Maréchal Juin, F-14050, Caen,
France
(3)
Department of Physics, University of Florida, Gainesville, FL 32611-8440, USA
We study chaotic scattering outside the wide band limit, as the Fermi energy E F approaches
the band edges E B of a one-dimensional lattice embedding a scattering region of M sites [1].
The Hamiltonian H M of this region is taken from the Cauchy orthogonal ensemble. The
scattering is chaotic at E F if the average level density per site of H M at E F describes a semicircle
as E F varies inside the conduction band. The edges of this semi-circle coincide with the
band edges E B . We show that the delay-time and thermopower distributions differ near the
edges from the universal expressions valid in the bulk [2]. To obtain the asymptotic universal
forms of these edge distributions, one must keep constant the energy distance E F – E B
measured in unit of the same energy scale (proportional to M -1/3 ) which is used for rescaling

Tuesday
the energy level spacings at the spectrum edges of large Gaussian matrices. In particular the
delay-time and the thermopower have the same universal edge distributions for arbitrary M
as those for an M=2 scatterer, which we obtain analytically.
[1] A. Abbout, G. Fleury, J.-L. Pichard and K. Muttalib, in preparation
[2] P. W. Brouwer, K. M. Frahm and C. W. J. Beenakker, Quantum Mechanical Time-Delay
Matrix in Chaotic Scattering, Phys. Rev. Lett. 78, 4737 (1997)
__________________________________________________________________________
Harvesting fluctuations at electrical hot spots
Rafael Sánchez
Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), Madrid, Spain
In electrical circuits hot spots occur naturally at places where energy is dissipated. Here we
propose a controlled experiment which can demonstrate the appearance of directed current
as a consequence of a hot spot. We investigate transport generated in Coulomb coupled
electrical conductors from excess electric or thermal fluctuations at the coupling capacitance.
If one of the conductors supports a bias voltage, out of equilibrium charge fluctuations
remove detailed balance in the unbiased system manifested in a drag current. Non linear
fluctuation relations can nevertheless be obtained [1].
Coulomb coupled conductors permit separate directions of the heat and current flux [2]. In
our model, one of the conductors is connected via only one lead to a hot reservoir. The other
conductor is connected to two leads. Such a geometry can be used for detection of non
linear heat fluctuations [3]. We investigate the minimal conditions needed to generate
directed current flow for a system of two quantum dot conductors in which both energy and
charge states are quantized. In quantum dots energy to current conversion can be optimal
with one electron transferred for every heat quantum given up by the hot reservoir. We show
that at the point of maximum power extraction the efficiency approaches one half of the
Carnot efficiency. However, the generated power is small.
Larger currents can be generated in a chaotic mesoscopic cavity coupled to two leads. Non
linearities due to energy dependent contact transmission to leads are responsible for the
rectification of thermal fluctuations in a coupled hot cavity, leading to an electrical current [4].
The maximum power produced by the system will be discussed.
[1] R. Sánchez, R. López, D. Sánchez, and M. Büttiker, Mesoscopic Coulomb drag, broken
detailed balance and fluctuation relations, Phys. Rev. Lett. 104 076801 (2010)
[2] R. Sánchez, and M. Büttiker, Optimal energy quanta to current conversion, Phys. Rev. B
83 085428 (2011)
[3] R. Sánchez, and M. Büttiker, Detection of single electron heat transfer statistics,
arXiv:1207:2587
[4] B. Sothmann, R. Sánchez, A.N. Jordan, and M. Büttiker, Rectification of termal
fluctuations in a chaotic cavity heat engine, Phys. Rev. B 85 205301 (2012)

Tuesday
Scattering theory of nonlinear thermoelectric transport
David Sánchez
Institute for Cross-Disciplinary Physics and Complex Systems IFISC (UIB-CSIC), E-07122
Palma de Mallorca, Spain
We discuss nonlinear transport properties of quantum conductors in response to both
electrical and thermal driving forces. Within scattering approach, we determine the
nonequilibrium screening potential of a generic mesoscopic system and find that its response
is dictated by particle and entropic injectivities which describe the charge and entropy
transfer during transport. We illustrate our model analyzing the voltage and thermal
rectification of a resonant tunneling barrier. Importantly, we investigate interaction induced
contributions to the thermopower in the presence of large temperature differences [1].
[1] D. Sánchez and R. López, arxiv:1209.1264 (preprint, 2012).
__________________________________________________________________________
Magnon-driven quantum-dot heat engine
Björn Sothmann, Markus Büttiker
Département de Physique Théorique, Université de Genève, CH-1211 Genève 4,
Switzerland
The concept of harvesting energy from the environment to power small devices has become
increasingly popular. Recently, there was a particular interest in quantum dot systems that
generate electrical currents from thermal fluctuations [1,2]. The main focus of the emergent
field of spin caloritronics is the idea to drive and control spin currents by heat.
Here, we discuss a setup consisting of a single-level quantum dot coupled to two
ferromagnetic metals and a ferromagnetic insulator held at different temperatures which
combines the ideas of energy harvesting and spin caloritronics. We demonstrate that this
nanoengine can act as an optimal heat to spin-polarized charge current converter in an
antiparallel geometry, while it acts as a heat to pure spin current converter in the parallel
case. We discuss the maximal output power of the device and its efficiency [3].
[1] R. Sánchez, M. Büttiker, Optimal energy quanta to current conversion, PRB 83, 085428
(2011)
[2] B. Sothmann, R. Sánchez, A. N. Jordan, M. Büttiker, Rectification of thermal fluctuations
in a chaotic cavity heat engine, PRB 85, 205301 (2012)
[3] B. Sothmann, M. Büttiker, Magnon-driven quantum-dot heat engine, EPL 99 27001 (2012)

Tuesday
Electron refrigeration by nonadiabatic pumping and related questions on quantum
cooling
Fernando Sols
Universidad Complutense de Madrid
Some features of nonadiabatic electron heat pumps are studied and connected to general
questions on quantum cooling [1,2]. Inelastic reflection is shown to contribute to heating if the
external driving signal is time symmetric. Within the tunneling limit, it is shown that electron
cooling still occurs if the coherent ac source is replaced by a sufficiently hot thermal bath. A
comparison with related refrigeration setups is presented [3,4]. The quantum of cooling
power (πk B T) 2 /6h$ is shown to be an upper limit to the cooling rate per transport channel in
the presence of an arbitrary driving signal. The question is addressed of whether there is a
universal limit to the cooling rate of a quantum system.
[1] M. Rey, M. Strass, S. Kohler, P. Hänggi, F. Sols. Nonadiabatic electron heat pump, Phys.
Rev. B 76, 085337 (2007).
[2] F. Sols. Aspects of quantum cooling in electron and atom systems, Physica E 42, 466
(2010), Proc. FQMT’08.
[3] J.P. Pekola, F.W.J. Hekking. Normal-Metal-Superconductor Tunnel Junction as a
Brownian Refrigerator, Phys. Rev. Lett. 98, 210604 (2007).
[4] B. Cleuren, B. Rutten, C. Van den Broeck. Cooling by Heating: Refrigeration Powered by
Photons, Phys. Rev. Lett. 108, 120603 (2012).
__________________________________________________________________________
Giant thermopower and figure of merit in single-molecule junctions
Colin Lambert
Department of Physics, Lancaster University, Lancaster, UK, LA1 4YB
Single molecules connected to nanogap electrodes provide an opportunity for tuning
electrical and thermoelectrical properties at the sub-nanometre scale. In this talk I shall
present a study of the electronic contribution to thermopower S and the dimensionless figure
of merit ZT in molecules sandwiched between gold electrodes. I shall show that for
molecules with pendant groups, the shape of the transmission coefficient can be modified by
Fano resonances near the Fermi energy, which can be tuned to produce huge increases in S
and ZT. Tuning of transmission resonances can also be achieved by varying the coupling
between molecular-scale structures. As an example, results will be presented for electron
transport through single and double C60s. It will be shown that the thermopower and figure
of merit for the latter is enhanced, compared with the former.
[1] Giant thermopower and figure of merit in single-molecule devices, C. M. Finch, V. M.
García-Suárez, and C. J. Lambert, Phys. Rev. B 79, 033405 (2009)
[2] Control of electron transport through Fano resonances in molecular wires, T.A.
Papadopoulos, I.M. Grace and C.J. Lambert, Phys. Rev. B 74 193306 (2006)

Wednesday
Wednesday, October 24
Thermoelectric properties of strongly correlated quantum systems
Antoine Georges
Collège de France, Paris - Ecole Polytechnique, Palaiseau, France - Université de Genève,
Suisse
Materials with strong electronic correlations, especially transition-metal oxides, have received
increasing attention as possible thermoelectrics. An interesting regime is that of intermediate
to high temperatures, where enough entropy is unquenched. I will describe here the
theoretical understanding of the temperature–dependence of the Seebeck coefficient for
simple models of interacting electrons, as well as selected experimental results. On another
note, I will present a recent proposal for studying fundamental aspects of thermoelectric
effects using ultra-cold atomic gases.
__________________________________________________________________________
Thermopower and thermoelectric efficiency in systems with broken time-reversal
symmetry
Giuliano Benenti
Center for Nonlinear and Complex Systems, Università degli Studi dell'Insubria, Via Valleggio
11, 22100 Como, Italy
We show that in systems with broken time-reversal symmetry the maximum efficiency and
the efficiency at maximum power are both determined by two parameters: a ``figure of merit''
which generalizes the thermoelectric figure of merit ZT, and an asymmetry parameter, which
becomes relevant when the thermopower is not an even function of the magnetic field. In
contrast to the time-symmetric case, the figure of merit is bounded from above; nevertheless
the Carnot efficiency can be reached at lower and lower values of the figure of merit as the
asymmetry parameter increases. Moreover, the Curzon-Ahlborn limit for efficiency at
maximum power can be overcome within linear response. We show that a weak magnetic
field generally improves either the efficiency of thermoelectric power generation or of
refrigeration, the efficiencies of the two processes being no longer equal when a magnetic
field is added. Finally, we discuss the thermopower asymmetry and thermoelectric efficiency
for a three-dot ring pierced by an Aharonov-Bohm flux, for random matrix models, and for
more abstract transmission models.
[1] K. Saito, G. Benenti and G. Casati, A microscopic mechanism for increasing
thermoelectric efficiency, Chem. Phys. 375, 508 (2010)
[2] G. Benenti and G. Casati, Increasing thermoelectric efficiency: dynamical models unveil
microscopic mechanisms, Phil. Trans. R. Soc. A 369, 466 (2011)
[3] G. Benenti, K. Saito and G. Casati, Thermodynamic bounds on efficiency for systems with
broken time-reversal symmetry, Phys. Rev. Lett. 106, 230602 (2011)

Wednesday
[4] K. Saito, G. Benenti, G. Casati and T. Prosen, Thermopower with broken time-reversal
symmetry, Phys. Rev. B 84, 201306(R) (2011)
[5] V. Balachandran, R. Bosisio and G. Benenti, Validity of Wiedemann Franz law in small
molecular wires, Phys. Rev. B 86, 035433 (2012)
[6] M. Horvat, T. Prosen, G. Benenti and G. Casati, Railway switch transport model, preprint
arXiv:1207.6014v1 [cond-mat.mes-hall]
Heat and Nanotechnologies : Focus on Thermoelectricity
Sebastian Volz
Laboratoire d'Energétique Moléculaire et Macroscopique, UPR CNRS 288 ,Ecole Centrale
Paris
Nanotechnologies were supposed to give birth to a new revolution based on the design of
new molecular nanorobot but finally consisted in the fabrication of new materials including
nanostructures with enhanced properties. Thermoelectric materials are one of the outcomes
and will be addressed in the talk.
An introduction on nanotechnologies at broad and on nanoscale heat transport applications
will be provided. Then a focus on thermoelectric materials will include a presentation of the
electrical physical effects as well as the main thermoelectric applications. Heat conduction
effects at nanoscales will then be presented and detailed for several key nanostructures
(nanowires, superlattices and nanoparticles). The corresponding achievements in terms of
figure of merit will finally be presented.

Thursday
Thursday, October 25
Observation of neutral modes in the fractional quantum Hall regime
Moty Heiblum
Current propagates in the fractional quantum Hall effect (FQHE) regime along the edges of
the two-dimensional-electron gas (2DEG) via chiral edge modes with a chirality dictated by
the applied magnetic field. Early predictions suggested the presence of counter propagating
edge modes for some fractional states, the so called, hole-conjugate states, such as ½

Thursday
[3] B. A. Bernevig, T. L. Hughes, and S. -C. Zhang, Science 314, 1757 (2006).
[4] M. Konig et al., Science 318, 766 (2007).
[5] C.-X. Liu et al., Phys. Rev. B 83, 035407 (2011).
[6] D. Chevallier et al., Phys. Rev. B 82, 155318 (2010).
[7] B. J. Overbosch and C. Chamon, Phys. Rev. B 80, 035319 (2009).
[8] J. C. Y. Teo and C. L. Kane, Phys. Rev. B 79, 235321 (2009).
[9] A. Strom and H. Johannesson, Phys. Rev. Lett. 102, 096806 (2009).
[10] T. L. Schmidt, Phys. Rev. Lett. 107, 096602 (2011).
_________________________________________________________________________
Spinful Majorana fermions and magnetoelectricity in junctions of 1D quantum wiresuperconductor
heterostructures
Panagiotis Kotetes 1 , A. Shnirman 2 , G. Schön 1
1 Institut für Theoretische Festkörperphysik, Karlsruhe Institute of Technology, 76128
Karlsruhe
2 Institut für Theorie der Kondensierten Materie, Karlsruhe Institute of Technology, 76128
Karlsruhe
Recently, the interest in topological quantum computing has grown due to the appearance of
promising platforms for realizing the long sought Majorana fermions. Among the proposals
that seem suitable for engineering Majorana fermions, the most prominent involves a 1D
semiconducting quantum wire in proximity to a bulk s-wave superconductor, where in
addition a Zeeman field is applied. Here we investigate the Josephson effect in TNT and
NTN junctions, consisting of topological (T) and normal (N) phases of semiconductorsuperconductor
1D heterostructures in the presence of a Zeeman field [1]. A key feature of
our setup is that, in addition to the variation of the phase of the superconducting order
parameter, we allow the orientation of the magnetic field to change along the junction. We
find a novel magnetic contribution to the Majorana Josephson coupling that permits the
Josephson current to be tuned by changing the orientation of the magnetic field along the
junction. We also predict that a spin current can be generated by a finite superconducting
phase difference, rendering these materials potential candidates for spintronic applications.
Finally, this new type of coupling not only constitutes a unique fingerprint for the existence of
Majorana fermions but also provides an alternative pathway for manipulating and braiding
topological qubits in networks of wires.
[1] P. Kotetes, A. Shnirman, G. Schön, arXiv:1207.2691.

Thursday
Andreev reflection from a topological superconductor with chiral symmetry
M. Diez, J. P. Dahlhaus, M. Wimmer, C. W. J. Beenakker
Instituut-Lorentz, Universiteit Leiden, P.O. Box 9506, 2300 RA Leiden, The Netherlands
Chiral symmetry (H -> -H if e h) of the Hamiltonian of electron-hole (e-h) excitations in an
N-mode superconducting wire is associated with a topological quantum number Q ∈ Z
(symmetry class BDI). In Ref. [1] we show that Q=Tr(r he ) equals the trace of the matrix of
Andreev reflection amplitudes, providing a link with the electrical conductance G. We derive
G=(2e 2 /h)|Q| for |Q|=N,N-1, and more generally provide a Q-dependent upper and lower
bound on G. We calculate the probability distribution P(G) for chaotic scattering, in the
circular ensemble of random-matrix theory, to obtain the Q-dependence of weak localization
and mesoscopic conductance fluctuations. We investigate the effects of chiral symmetry
breaking by spin-orbit coupling of the transverse momentum (causing a class BDI-to-D
crossover), in a model of a disordered semiconductor nanowire with induced
superconductivity. For wire widths less than the spin-orbit coupling length, the conductance
as a function of chemical potential can show a sequence of 2e 2 /h steps - insensitive to
disorder.
[1] M. Diez, J. P. Dahlhaus, M. Wimmer, C. W. J. Beenakker, Andreev reflection from a
topological superconductor with chiral symmetry, Phys. Rev. B 86 094501 (2012)
__________________________________________________________________________
Zero-bias conductance peak from weak antilocalization in a Majorana nanowire
Dmitry I. Pikulin*, J. P. Dahlhaus*, M. Wimmer*, H. Schomerus', and C. W. J. Beenakker*
*Instituut-Lorentz, Universiteit Leiden, P.O. Box 9506, 2300 RA Leiden, The Netherland,
'Department of Physics, Lancaster University, Lancaster, LA1 4YB, United Kingdom
We show [1] that weak antilocalization by disorder coexists with resonant Andreev reflection
by Majorana zero-mode, both producing zero-voltage conductance peak of order e 2 /h in a
superconducting nanowire. The peak is widely believed to be the smoking gun signature of
the Majorana zero-mode [2], its observation has been reported [3]. We identify methods to
distinguish the Majorana resonance from the weak antilocalization effect.
[1] D. I. Pikulin, J. P. Dahlhaus, M. Wimmer, H. Schomerus, and C. W. J. Beenakker, arXiv
1206.6687 (2012)
[2] K. T. Law, P. A. Lee, and T. K. Ng, Phys. Rev. Lett. 103, 237001 (2009)
[3] V. Mourik, K. Zuo, S. M. Frolov, R. Plissard, E. P. A.M. Bakkers, and L. P. Kouwenhoven,
Science 336, 1003 (2012); M. T. Deng, C. L. Yu, G. Y. Huang, M. Larsson, P. Caroff, and H.
Q. Xu, arXiv:1204.4130 (2012); A. Das, Y. Ronen, Y. Most, Y. Oreg, M. Heiblum, and H.
Shtrikman, arXiv:1205.7073 (2012)

Thursday
Electronic standing waves on the surface of the topological insulator Bi 2 Te 3
P.Rakyta 1 , A.Pályi 2 , J.Cserti 1
1 Department of Physics of Complex Systems, Eötvös University, H-1117 Budapest, Pázmány
Péter sétány 1/A, Hungary
2 Department of Materials Physics, Eötvös University, H-1117 Budapest, Pázmány Péter
sétány 1/A, Hungary
A line defect on a metallic surface induces standing waves in the electronic local density of
states (LDOS). Asymptotically far from the defect, the wave number of the LDOS oscillations
at the Fermi energy is usually equal to the distance between nesting segments of the Fermi
contour, and the envelope of the LDOS oscillations shows a power-law decay as moving
away from the line defect. Here, we theoretically analyze the LDOS oscillations close to a
line defect on the surface of the topological insulator Bi 2 Te 3 , and identify an important
preasymptotic contribution with wave-number and decay characteristics markedly different
from the asymptotic contributions. The calculated energy dependence of the wave number of
the preasymptotic LDOS oscillations is in quantitative agreement with the result of a recent
scanning tunneling microscopy experiment [1].
[1] Z.Alpichshev, J.G.Analytis, J.-H.Chu, I.R.Fisher, Y.L.Chen, Z.X.Shen, A.Fang and
A.Kapitulnik, Phys. Rev. Lett. 104, 016401 (2010)
__________________________________________________________________________
How does Exact DFT compares with exact solutions in simple models of strongly
correlated electrons ?
Jaime Ferrer, Diego Carrascal
Departamento de Física, Universidad de Oviedo
We present analytic expressions for the exact density functional and Kohn-Sham
Hamiltonian of simple tight-binding models of correlated electrons. These are the single- and
double-site versions of the Anderson, Hubbard and spinless fermion models. The exact
exchange and correlation potentials keep the full non-local dependence on electron
occupations. The analytic expressions allow to compare the Kohn-Sham eigenstates of exact
density functional theory with the many-body quasi-particle states of these correlatedelectron
systems. The exact Kohn-Sham spectrum describes correctly many of the non-trivial
features of the many-body quasi-particle spectrum, as for example the precursors of the
Kondo peak. However, we find that some pieces of the quasi-particle spectrum are missing
because the many-body phase-space for electron and hole excitations is richer [1].
[1] D. Carrascal and J. Ferrer, Phys. Rev. B 85 045110 (2012)

Friday
Friday, October 2
Metallic phase of the quantum Hall effect in four-dimensional space
Jonathan M. Edge, J. Tworzydlo, C. W. J. Beenakker
Instituut-Lorentz, Universiteit Leiden, P.O. Box 9506, 2300 RA Leiden, The Netherlands
Institute of Theoretical Physics, Faculty of Physics, University of Warsaw, Hoza 69, 00--681
Warsaw, Poland
We study the phase diagram of the quantum Hall effect in four-dimensional (4D) space [1].
Unlike in 2D, in 4D there exists a metallic as well as an insulating phase, depending on the
disorder strength. The critical exponent ≈ 1.2 of the diverging localization length at the
quantum Hall insulator-to-metal transition differs from the semiclassical value = 1 of 4D
Anderson transitions in the presence of time-reversal symmetry. Our numerical analysis is
based on a mapping of the 4D Hamiltonian onto a 1D dynamical system, providing a route
towards the experimental realization of the 4D quantum Hall effect.
[1] J.M. Edge, J. Tworzydlo, C. W. J. Beenakker Metallic phase of the quantum Hall effect in
four-dimensional space arXiv:1206.0099 to be published in PRL (2012)
__________________________________________________________________________
Thermal metal in topological superconductors
Jakub Tworzydlo (1) , I. C. Fulga (2) , A. R. Akhmerov (2) , C.W.J. Beenakker (2) , B. Beri (3)
(1)
Faculty of Physics, University of Warsaw, Poland
(2)
Instituut-Lorentz, Universiteit Leiden, The Netherlands
(3)
TCM Group, Cavendish Laboratory, United Kingdom
The thermal quantum Hall effect appears in the absence of time-reversal symmetry in a
single layer of a chiral p-wave superconductor. The insulator-insulator transition associated
with this effect is generically present only for weak disorder. For stronger disorder we find a
transition to a delocalized phase, known as the thermal metal.
In contrast, for a helical superconductor in the presence of time-reversal symmetry the
transition between two topologically distinct thermal insulators occurs via the intervening
thermal metal phase, even for an arbitrarily weak disorder.
We present a detailed study of a phase diagram and the critical exponents for these
topologically induced transitions. We also point to an underling mechanism of Majorana
states formation in both chiral and helical systems.
[1] I. C. Fulga, A. R. Akhmerov, J. Tworzydlo, B. Beri, and C. W. J. Beenakker, Phys. Rev. B
86, 054505 (2012)
[2] M. V. Medvedyeva, J. Tworzydlo, and C. W. J. Beenakker, Phys. Rev. B 81, 214203
(2010)
[3] J. H. Bardarson, M. V. Medvedyeva, J. Tworzydło, A. R. Akhmerov, and C. W. J.
Beenakker, Phys.Rev. B 81, 121414(R) (2010)
[4] M. Wimmer, A. R. Akhmerov, M. V. Medvedyeva, J. Tworzydlo, C. W. J. Beenakker,
Phys. Rev. Lett. 105, 046803 (2010)

Friday
Nanoscale inhomogeneities in diluted magnetic systems : Effects on Curie
temperature and spontaneous magnetization
Akash Chakraborty (1,2) , Richard Bouzerar (3) , Paul Wenk (4) , Stefan Kettemann (2,5) , and
Georges Bouzerar (3,2)
(1)
Karlsruhe Institute of Technology, 76128 Karlsruhe, Germany
(2)
Jacobs University Bremen, 28759 Bremen, Germany
(3)
Institut Néel, CNRS, 38042 Grenoble Cedex 09, France
(4)
Universitaet Regensburg, 93040 Regensburg, Germany
(5)
Pohang University of Science and Technology (POSTECH), Pohang 790-784, South
Korea
The presence of nanoscale inhomogeneities has been experimentally evidenced in several
diluted magnetic systems, which in turn often leads to interesting physical phenomena.
Among them room-temperature ferromagnetism is one of the most interesting and sought
after topics in today’s emerging field of spintronics. However, until now, in the dilute regime it
has been difficult to obtain Curie temperatures larger than that measured in well annealed
samples of (Ga,Mn)As (∼190K for 12% doping). Here we suggest an innovative path to roomtemperature
ferromagnetism in diluted magnetic semiconductors. We theoretically show that
even a small concentration of nanoscale inhomogeneities can result in a gigantic increase of
the critical temperatures [1]. We give a plausible explanation for the wide variation of the
critical temperatures measured in (Ga,Mn)N and provide a better understanding of the likely
origin of very high Curie temperatures measured occasionally. We also show that nano-sized
clusters of magnetic impurities can lead to drastic effects on the temperature dependent
magnetization compared to that of homogeneously diluted compounds [2]. The unusual and
unconventional nature of the magnetization curves is found to strongly depend on the relative
concentration of the inhomogeneities as well as the effective range of the exchange
interactions.
[1] A. Chakraborty, R. Bouzerar, S. Kettemann, and G. Bouzerar, Nanoscale
inhomogeneities: A new path toward high Curie temperature ferromagnetism in diluted
materials, Phys. Rev. B 85 014201 (2012).
[2] A. Chakraborty, P. Wenk, R. Bouzerar, and G. Bouzerar, Spontaneous magnetizationin in
presence of nanoscale inhomogeneities in diluted magnetic systems, (submitted to Phys.
Rev. B).
__________________________________________________________________________
Onsager relations in a two-dimensional electron gas with spin-orbit coupling
Roberto Raimondi, Cosimo Gorini, and Peter Schwab
CNISM and Dipartimento di Fisica "E. Amaldi", via della Vasca Navale 84, Università Roma
Tre, 00146 Roma, Italy
Institut de Physique et Chimie des Matériaux de Strasbourg (UMR 7504), CNRS and
Université de Strasbourg, 23 rue du Loess, BP 43, F-67034 Strasbourg Cedex 2, France
Institut für Physik, Universität Augsburg, 86135 Augsburg, Germany
Theory predicts for the two-dimensional electrons gas with only Rashba spin-orbit interaction
a vanishing spin Hall conductivity and at the same time a finite inverse spin Hall effect. We
show how these seemingly contradictory results are compatible with the Onsager relations:
the latter do hold for spin and particle (charge) currents in the two-dimensional electron gas,
although (i) their form depends on the experimental setup and (ii) a vanishing bulk spin Hall

Friday
conductivity does not necessarily imply a vanishing spin Hall effect. We also discuss the
situation in which extrinsic spin orbit from impurities is present and the bulk spin Hall
conductivity can be different from zero.
[1] C. Gorini, R. Raimondi, P. Schwab, arXiv:1207.1289
__________________________________________________________________________
Spin-orbit coupling assisted by flexural phonons in graphene
H. Ochoa (1) , A. H. Castro Neto (2,3) , V. I. Fal'ko (4,5) , F. Guinea (1)
(1)
Instituto de Ciencia de Materiales de Madrid. CSIC. Sor Juana Inés de la Cruz 3. 28049
Madrid. Spain.
(2)
Graphene Research Centre and Physics Department, National University of Singapore, 2
Science Drive 3, 117542, Singapore.
(3)
Department of Physics, Boston University, 590 Commonwealth Ave., Boston MA 02215,
USA.
(4)
Physics Department, Lancaster University, Lancaster, LA1 4YB, UK.
(5)
DPMC, University of Geneva, 24 Quai Ernest-Ansermet, CH1211 Geneve 4, Switzerland
We present a complete analysis of the possible couplings between spins and flexural, out of
plane, vibrations [1]. From tight-binding models we obtain analytical and numerical estimates
of their strength. We show that dynamical effects, induced by quantum and thermal
fluctuations, significantly enhance the spin-orbit gap. We also compute the spin relaxation
rates due to flexural phonon scattering. Our results confirm that graphene is an excellent
candidate for spintronics devices.
[1] H. Ochoa, A. H. Castro Neto, V. I. Fal'ko, F. Guinea, Spin-orbit coupling assisted by
flexural phonons in graphene, arXiv:1209.4382 [cond-mat.mes-hall]
__________________________________________________________________________
Massless Dirac bosons in honeycomb plasmonic lattices
G. Weick, 1 C. Woollacott, 2 W.L. Barnes, 3 O. Hess, 4 E. Mariani 2
1
Institut de Physique et Chimie des Matériaux de Strasbourg, Université de Strasbourg &
CNRS
2
Centre for Graphene Science, School of Physics, University of Exeter
3
School of Physics, University of Exeter
4
The Blackett Laboratory, Department of Physics, Imperial College London
We consider a two-dimensional honeycomb lattice of metallic nanoparticles, each supporting
a localized surface plasmon, and study the properties of the collective plasmons resulting
from the near field dipolar interaction between the nanoparticles. We analytically investigate
the dispersion, the effective Hamiltonian and the eigenstates of the collective plasmons for
an arbitrary orientation of the individual dipole moments. When the polarization points close
to the normal to the plane the spectrum presents Dirac cones, similar to those present in the
electronic band structure of graphene. Moreover, we show that the corresponding
eigenstates of the collective plasmons represent Dirac-like massless bosonic excitations. We
further discuss how one can manipulate the Dirac points in the Brillouin zone and open a gap
in the collective plasmon dispersion by modifying the polarization of the localized surface
plasmons, paving the way for a fully tunable plasmonic analogue of graphene.

Friday
Electron focusing in grapheme
Csaba Péterfalvi 1,2 , László Oroszlány 1 , József Cserti 1 , Colin Lambert 2
1 Department of Physics of Complex Systems, Eötvös University, Budapest, H-1117,
Hungary
2 Department of Physics, Lancaster University, Lancaster, LA1 4YB, UK
We propose an implementation of a valley selective electronic Veselago lens, as a planar
potential step in bilayer graphene. We demonstrate that low energy electrons radiating from
a point source and being scattered by an appropriately oriented potential step can be
focused again coherently within the same band. The phenomenon is due to the negative
refraction index which is a consequence of the anisotropy in the dispersion relation caused
by the trigonal warping effect. We also consider an effective Hamiltonian in which the
electron-electron interaction [1], as well as external mechanical strain [2] is taken into
account, and we show how this affects the focusing phenomenon. Recent studies on the
electron-phonon interaction in bilayer graphene [3] suggest that the electrons' free path can
be long enough even on room temperatures to enable the focusing.
[1] Y. Lemonik, I. L. Aleiner, C. Toke, and V. I. Fal’ko, Spontaneous symmetry breaking and
Lifshitz transition in bilayer graphene, Phys. Rev. B 82, 201408 (2010)
[2] M. Mucha-Kruczyński, I. L. Aleiner and V. I. Fal’ko, Strained bilayer graphene: Band
structure topology and Landau level spectrum, Phys. Rev. B 84, 041404 (2011)
[3] K. M. Borysenko, J. T. Mullen, X. Li, Y. G. Semenov et al, Electron-phonon interactions in
bilayer graphene, Phys. Rev. B 83, 161402 (2011)
__________________________________________________________________________
Theory of scanning gate microscopy
C. Gorini 1 , R. A. Jalabert 1 , W. Szewc 1 , S. Tomsovic 2 and D. Weinmann 1
1 Institut de Physique et Chimie des Matérieux de Strasbourg, UMR 7504, CNRS-UdS, 23 rue
du Loess, BP 43, 67034 Strasbourg Cedex 2, France
2 Department of Physics and Astronomy, PO Box 642814, Washington State University,
Pullman, WA 99164-2814, USA
The conductance change due to a local perturbation in a phase-coherent nanostructure is
calculated [1]. The general expressions to first and second order in the perturbation are
applied to the scanning gate microscopy of a two-dimensional electron gas containing a
quantum point contact. The relation between the conductance change and the local current
density is discussed relying on an extension of the Szafer-Stone model for a constriction [2].
[1] R. A. Jalabert, W. Szewc, S. Tomsovic and D. Weinmann, What is measured in the
scanning gate microscopy of a quantum point contact? Phys. Rev. Lett. 105 166802 (2010)
[2] A. Szafer and A. D. Stone, Theory of Quantum Conduction through a Constriction Phys.
Rev. Lett. 62 300 (1989)

Friday
Electron interferometry with a Quantum Point Contact: Effect of electron-electron
interaction and temperature
Andrii Kleshchonok, Geneviève Fleury, Jean-Louis Pichard
Service de Physique de l’Etat Condensé, IRAMIS / SPEC, CEA Saclay, 91191 Gif-sur-
Yvette, France
Motivated by experiments recently made in Harvard [1], Stanford [2], Zurich [3] and Grenoble
[4], we study a simplified model for describing an electron interferometer formed with a
quantum point contact and the depletion region induced by the charged tip of a scanning
gate microscope. The contact is made of a single site with Hubbard interaction U (Anderson
impurity) coupling two semi-infinite square lattices. A local moment [5] can take place in the
contact above the Kondo temperature. We study how this moment can be manipulated when
one scans the tip around the contact. We discuss also how the conductance of this
interferometer depends on the location the tip, on the strength U of the interaction and on the
temperature, in regimes where the Hartree-Fock approximation remains valid [6]. In certain
cases, an enhancement of the interference fringes can be yielded by an increase of the
temperature [7] or an increase of the strength U of the interaction.
[1] M.A. Topinka, et al. Coherent Branched Flow in a Two-Dimensional Electron Gas, Nature
410 183 (2001)
[2] M. P. Jura, et al. Unexpected features of branched flow through high-mobility twodimensional
electron gases , Nature Physics 3 841-845 (2007)
[3] A. A. Kozikov, et al. Interference of electrons in backscattering through a quantum point
contact, arXiv:1206.1371v1
[4] M. G.Pala , et al. Scanning gate microscopy of quantum rings: effects of an external
magnetic field and of charged defects, Nanotechnology 20, 26 (2009)
[5] Anderson P. W. Localized Magnetic States in Metals, Physical Review 124 41-53 (1961)
[6] Tsvelick A. M., Wiegmann P. B. Exact results in the theory of magnetic alloys, Advances
in Physics 32 453 (1983)
[7] About A., Lemarié G., Pichard J.-L. Thermal Enhancement of Interference Effects in
Quantum Point Contacts Phys. Rev. Lett. 106 156810 (2011)
__________________________________________________________________________
Symmetry-induced interference effects in metalloporphyrins wires
R.Ferradás 1,2 , V.M.García-Suárez 1,2,3 and J.Ferrer 1,2,3
1
Departamento de Física, Universidad de Oviedo, 33007 Oviedo, Spain
2
Nanomaterials and Nanotechnology Research Center, CSIC-Universidad de Oviedo, Spain
3
Department of Physics, Lancaster University, Lancaster LA1 4YW, United Kingdom
Organo-metallic molecular structures where a single metallic atom is embedded in the
organic backbone are ideal systems to study the effect of strong correlations on their
electronic structure. In this work we calculate the electronic and transport properties of a
series of metalloporphyrin molecules sandwiched by gold electrodes using a combination of
density functional theory and scattering theory. The impact of strong correlations at the
central metallic atom is gauged by comparing our results obtained using conventional DFT
and DFT+U approaches. The zero bias transport properties may or may not show spinfiltering
behavior, depending on the nature of the d state closest to the Fermi energy. The
type of d state depends on the metallic atom and gives rise to interference effects that
produce different Fano features. The inclusion of the U term opens a gap between the d
states and changes qualitatively the conductance and spin-filtering behavior in some of the

Friday
molecules. We explain the origin of the quantum interference effects found as due to the
symmetry-dependent coupling between the d states and other molecular orbitals and
propose the use of these systems as nanoscale chemical sensors. We also demonstrate that
an adequate treatment of strong correlations is really necessary to correctly describe the
transport properties of metalloporphyrins and similar molecular magnets.
[1] D. Dolphin, The Porphyrins Handbook, Academic, New York (1978)
[2] M. Liao and S.Scheiner, Electronic structure and bonding in metal porphyrins, Journal of
chemical Physics 117, 205 (2002)
[3] J. Otsuki, STM studies on Porphyrins, Chemical Review 254, 2311 (2010)
[4] V.I. Anisimov, J. Zaanen and O.K. Andersen, Band theory and Mott insulators: Hubbard
instead of Stoner I, Physical Review B 44, 943 (1991)
[5] A.I. Liechtenstein,V.I. Anisimov and J. Zaanen, DFT and strong interactions: Orbital
ordering in Mott-Hubbard insulators, Physical Review B 52, 5467 (1995)
[6] C. Tablero, Representations of the occupation number matrix on the LDA/GGA+U
method, J. Phys.:Condensed Matter 20, 325205
[7] M. Cococcioni and S. Gironcoli, Linear response approach to the calculation of the
effective interaction parameters in LDA+U method, Physical Review B 71, 035105 (2005)
[8] R.E. Sparks, V.M. García-Suárez, D.Zs. Manrique and C.J. Lambert, Quantum
interference in single molecule electronic systems, Physical Review B 83, 075437 (2011)
__________________________________________________________________________
Ac magnetic fields coupled to spin qubits
Álvaro Gómez León and Gloria Platero
Sor Juana Inés de la Cruz, 3, Cantoblanco, 28049, Madrid, Spain
Quantum systems coupled to periodic ac electric or magnetic fields present new interesting
coherence properties not present in the undriven system. We will show that the presence of
an external periodic ac magnetic field applied to a two coupled two-level systems, such as a
double quantum dot, is able to induce charge localization, spin locking or both, by tuning the
ac field parameters, i.e., the frequency, intensity or phase difference, as well as by tuning its
polarization.
In contrast with ac electric fields, the possibility of induce dynamical spin locking will allow to
freeze the spin projection of the initial state for some values of the parameter space [2,3]. We
show how the symmetries of the Hamiltonian in the presence of the driving field influence the
quasi-energy spectrum and how they determine the electronic charge and spin dynamics.
Finally we discuss how the application of an ac magnetic field to these systems allows to
tune the topological properties for both the adiabatic and the non adiabatic regime [4]. Our
results generalize those on geometrical phases for the spin by Berry [5] including the spatial
degree of freedom and spatial anisotropy for the magnetic field.
[1] Charge localization and dynamical spin locking in double quantum dots driven by ac
magnetic fields, A. Gómez-León and G. Platero, Phys. Rev. B (Rapid Communications) 84,
121310 (2011).
[2] Transport blocking and topological phases using ac magnetic fields, A. Gómez-León and
G. Platero, Phys. Rev. B 85, 245319 (2012).
[3] Topological phases in adiabatic and nonadiabatic driven systems, A. Gómez-León and G.
Platero, Phys. Rev. B 86, 115318 (2012).
[4] Quantal Phase Factors Accompanying Adiabatic Changes, M. V. Berry, Proc. R. Soc.
Lond. A 392, 45-57 (1984).

Friday
Nonequilibrium transport response from equilibrium transport theory
Víctor García Suárez and Jaime Ferrer
Department of Physics, University of Oviedo and CINN (CSIC).Oviedo (Spain).
Department of Physics, Lancaster University. Lancaster (UK).
We propose a simple scheme [1] that describes accurately essential non-equilibrium effects
in nanoscale electronics devices using equilibrium transport theory. The scheme, which is
based on the alignment and dealignment of the junction molecular orbitals with the shifted
Fermi levels of the electrodes, simplifies drastically the calculation of current-voltage
characteristics compared to typical non-equilibrium algorithms. We probe that the scheme
captures a number of non-trivial transport phenomena such as the negative differential
resistance and rectification effects. It applies to those atomic-scale junctions whose relevant
states for transport are spatially placed on the contact atoms or near the electrodes.
[1] V. M. García-Suárez and J. Ferrer, Nonequilibrium transport response from equilibrium
transport theory, Phys. Rev. B. 86 125456 (2012)
__________________________________________________________________________
Quantum chaos in disordered graphene
Spiros Evangelou
University of Ioannina, Physics Department, Ioannina-45110 Greece
I shall report on the energy-level statistics in disordered graphene lattices of various
shapes[1] close to the Dirac point. The level-spacing distribution function, shown for various
flakes with armchair, zigzag and Klein edges, will be consistent with weakly chaotic behavior.
The obtained level-spacing distribution is also related to critical fractal eigenstates while
Anderson localization occurs for strong disorder.
[1] H.Amanatidis, I.Kleftogiannis, D.E.Katsanos and S.N.Evangelou (to be submitted).
.

Posters
Posters
Ab-initio study of the thermopower of biphenyl-based single-molecule junctions
M. Bürkle 1, 2 , L. A. Zotti 3 , J. K. Viljas 4, 5 , D. Vonlanthen 6 , A. Mishchenko 7
T. Wandlowski 7 M. Mayor 2, 6, 8 G. Schön 1, 2, 8 1, 2, 9
and F. Pauly
1
Institute of Theoretical Solid State Physics, Karlsruhe Institute of Technology, D-76131
Karlsruhe, Germany
2
DFG Center for Functional Nanostructures, Karlsruhe Institute of Technology, D-76131
Karlsruhe, Germany
3
Departamento de Física Teórica de la Materia Condensada,
Universidad Autónoma de Madrid, E-28049 Madrid, Spain
4
Low Temperature Laboratory, Aalto University, P.O. Box 15100, FIN-00076 Aalto, Finland
5
Department of Physics, P.O. Box 3000, FIN-90014 University of Oulu, Finland
6
Department of Chemistry, University of Basel, CH-4056 Basel, Switzerland
7
Department of Chemistry and Biochemistry, University of Bern, CH-3012 Bern, Switzerland
8
Institute for Nanotechnology, Karlsruhe Institute of Technology, D-76344 Eggenstein-
Leopoldshafen, Germany
9
Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720
By employing ab initio electronic-structure calculations combined with the nonequilibrium
Green's function technique, we study the dependence of the thermopower Q on the
conformation in biphenyl-based single-molecule junctions. For the series of experimentally
available biphenyl molecules, alkyl side chains allow us to gradually adjust the torsion angle
between the two phenyl rings from 0 ° to 90 ° and to control in this way the degree of π-
electron conjugation. Studying different anchoring groups and binding positions, our theory
predicts that the absolute values of the thermopower decrease slightly towards larger torsion
angles, following an a+bcos2 dependence. The anchoring group determines the sign of Q
and a,b simultaneously. Sulfur and amine groups give rise to Q,a,b>0, while for cyano,
Q,a,b

Posters
Non-adiabatically driven electron in quantum wire
T. Cadez 1 , J. H. Jefferson 2 and A. Ramsak 1,3
1
J. Stefan Institute, Ljubljana, Slovenia
2
Department of Physics, Lancaster University, Lancaster LA1 4YB, UK
3
Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana, Slovenia
An exact solution is derived for the wave function of an electron in a semiconductor quantum
wire with spin-orbit interaction and driven by external time dependent harmonic confining
potential [1]. The formalism allows analytical expressions for various quantities to be derived,
such as spin and pseudo-spin rotations, energy and occupation probabilities for excited
states. It is demonstrated how perfect spin and pseudo-spin flips can be achieved at high
frequencies of order , the confining potential level spacing. By an appropriately chosen
driving term, spin manipulation can be exactly performed far into the non-adiabatic regime.
Implications for spin-polarised emission and spin-dependent transport are also discussed.
[1] T. Cadez, J. H. Jefferson and A. Ramsak, Non-adiabatically driven electron in quantum
wire, arXiv: 1208.5359
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Spin-orbit effects in nanowire-based wurtzite semiconductor quantum dots
Guido Intronati (1,2,3) , Pablo Tamborenea (1) , Rodolfo Jalabert (2) , Dietmar Weinmann (2)
(1) Departamento de Física, Universidad de Buenos Aires, Ciudad Universitaria, Pab. I,
C1428EHA Buenos Aires, Argentina
(2) Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504, CNRS-UdS, 23
rue du Loess, BP 43, 67034 Strasbourg Cedex 2, France
(3) Service de Physique de l'Etat Condensé CNRS URA 2464, CEA Saclay, 91191 Gif-sur-
Yvette, France
We study the effects of spin-orbit interaction on the electronic states and spin relaxation
rates of cylindrical quantum dots defined on wurtzite quantum wires. The linear and cubic
contributions of the bulk Dresselhaus spin-orbit coupling are taken into account, along with
the influence of an external magnetic field. An analytic solution for the electronic states that
was previously found for cylindrical pillbox zincblende quantum dots with Rashba interaction
is extended here to the case of wurtzite dots. The energy spectrum is computed, and the
electronic states for InAs are characterized. This may be a useful aspect of this compound
from the point of view of applications to spin manipulation.

Posters
Nonclassical photon-pair production in a voltage-biased Josephson junction
Juha Leppäkangas 1 , Göran Johansson 1 , Michael Marthaler 2 , and Mikael Fogelström 1
1
Microtechnology and Nanoscience, MC2, Chalmers University of Technology, SE-412 96
Göteborg, Sweden
2
Institut für Theoretische Festkörperphysik and DFG-Center for Functional Nanostructures
(CFN), Karlsruhe Institute of Technology, D-76128 Karlsruhe, Germany
We investigate electromagnetic radiation emitted by a small voltage-biased Josephson
junction connected to a superconducting transmission line. For weak tunneling couplings and
frequencies below the well known emission peak at the Josephson frequency (2eV/h), extra
radiation is triggered by quantum noise in the electromagnetic environment. For typical ohmic
transmission lines, the corresponding photon flux spectrum becomes symmetric around half
the Josephson frequency, indicating that the photons are predominately created in pairs. By
establishing an input-output formalism for the microwave field in the transmission line, we
give further evidence for this non-classical photon pair production, demonstrating that it
violates the classical Cauchy-Schwarz inequality for two-mode flux cross correlations. In
connection to recent experiments [1], we also consider a stepped transmission line, where
resonances increase the signal-to-noise ratio.
[1] M. Hofheinz, F. Portier, Q. Baudouin, P. Joyez, D. Vion, P. Bertet, P. Roche, and D.
Esteve Bright Side of the Coulomb Blockade, Phys. Rev. Lett. 106 217005 (2011)
__________________________________________________________________________
Gap Generation in Topological Insulator Surface States by non-Ferromagnetic
Magnets
László Oroszlány 1 , Alberto Cortijo 2
1
Department of Physics of Complex Systems, Eotvos University,
H-1117 Budapest, Pázmány Péter sétány 1/A, Hungary
2
Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, 28049 Madrid, Spain.
Within a tight binding approach, it is shown that, contrary to the naive expectation, single
particle spectral gaps can be opened on the surface states of three dimensional topological
insulators by using commensurate out- and in-plane antiferromagnetic or ferromagnetic
insulating thin films [1].
[1] L. Oroszlány, A. Cortijo arXiv:1208.4615
__________________________________________________________________________
Optical conductivity of bilayer graphene in the far-infrared (FIR) spectral range
Gábor Széchenyi, József Cserti
Department of Physics of Complex Systems, Eötvös University, Budapest, Hungary
Using Kubo formula we study theoretically the frequency dependent optical conductivity in
bilayer graphene with symmetry breaking mechanisms. We demonstrate that in the FIR
spectral range (1.2-80 meV) the spectrum is strongly sensitive to the rate of the symmetry
breaking, the trigonal warping and the polarization of the light. We show analytically a
connection between the minimal conductivity and the zero frequency limit of the optical
spectrum.

Posters
Entanglement and the Kondo effect in triple quantum dots
S. B. Tooski 1, 2, 3 , B. Bulka 3 , R. Zitko 1,2 , and A. Ramsak 1, 2
1 Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana, Slovenia
2 J. Stefan Institute, Ljubljana, Slovenia
3 Institute of Molecular Physics, Polish Academy of Sciences, ul. M. Smoluchowskiego 17,
Poznan, Poland
We analyze a system of triple quantum dots in a triangular geometry, in which one of the
quantum dots is connected to metallic leads, Fig. 1. We expect that the Kondo effect
between the leads and central dot C (with intra-dot Coulomb interactions) can induce perfect
spin entangled states between dots A and B (dots without intra-dot interactions). Using
Wilson’s numerical renormalization group technique [1], we investigate various spin-spin
correlation functions, probabilities for antiparallel and parallel spin alignment, and the
concurrence [2] to quantify quantum entanglement in the triple quantum dot system [3], in the
regime where each dot is essentially singly occupied by adjusting a global back-gate voltage.
As a consequence of quantum phase transition an abrupt switch between fully entangled and
separate states between A and B dots takes place. By tuning the interdot coupling t and the
dot-lead coupling Γ, one can switch abruptly ferromagnetic and antiferromagnetic interaction
between A and B dots. The effective Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction
between these dots is ferromagnetic in our simplified model. Here the spins order
ferromagnetically into a triplet state and undergo the S=1 Kondo screening at low
temperatures. This yields an uncompensated S=1/2 residual spin, and since half a unit of
spin is quenched by the conduction band via the Kondo effect, there clearly cannot be any
entanglement between the electrons on noninteracting dots. For t t , the antiferromagnetic
ordering wins and the electrons form an entangled singlet state on A and B dots. The
transition from the regime dominated by the RKKY interaction between A and B dots to the
Kondo singlet phase for C dot is in this case a true quantum phase transition and the
concurrence falls abruptly from C AB 1 to C AB 0.
c
A
t
B
t’ t’
L
C
R
Fig. 1. A triangle of quantum dots attached to the leads.
[1] R. Zitko, NRG_Ljubljana code; H. R. Krishna-murthy, J. W. Wilkins and K. G. Wilson,
Phys. Rev. B 21, 1003 (1980).
[2] A. Ramšak, J. Mravlje, R. Žitko, and J. Bonča, Phys. Rev. B 74, 241305(R) (2006); J.
Mravlje, A. Ramšak, and T. Rejec, Phys. Rev. B 73, 241305(R) (2006); T. Rejec and A.
Ramšak, Phys. Rev. B 68, 035342 (2003); A. Ramšak, I. Sega, and J. H. Jefferson, Phys.
Rev. A 74, 010304(R) (2006).
[3] W. Wang, Phys. Rev. B 78, 235316 (2008); A. K. Mitchell, T. F. Jarrold, and D. E. Logan
Phys. Rev. B 79, 085124 (2009).