Thermoelectric Properties of Fe0.2Co3.8Sb12-xTex ... - Physics
Thermoelectric Properties of Fe0.2Co3.8Sb12-xTex ... - Physics Thermoelectric Properties of Fe0.2Co3.8Sb12-xTex ... - Physics
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.
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TITLE: NUCLEOSYNTHESIS INSIDE GAMMARAY BURST ACCRETION DISKS<br />
AND ASSOCIATED OUTFLOWS<br />
AUTHORS: Indrani Banerjee, Banibrata Mukhopadhyay<br />
Department <strong>of</strong> <strong>Physics</strong>, Indian Institute <strong>of</strong> Science, Bangalore560012<br />
ABSTRACT<br />
Most popular models <strong>of</strong> long duration gammaray bursts invoke the core collapse <strong>of</strong><br />
rapidly rotating stars. The mass <strong>of</strong> the stars undergoing core collapse is usually<br />
greater than 20 solar mass in the main sequence. This core collapse results in the<br />
formation <strong>of</strong> black holes <strong>of</strong> 23 solar masses if it is <strong>of</strong> Schwarzschild type and 67<br />
solar masses if it is <strong>of</strong> maximally spinning Kerr type with an accretion disk around<br />
them. Such black holes accrete at the rate <strong>of</strong> 0.00110.0 solar masses per second. We<br />
investigate nucleosynthesis inside such gammaray burst accretion disks with<br />
accretion rate upto 0.1 solar mass per second since these disks are more likely to<br />
synthesize heavy elements. We show that varying accretion rate changes the<br />
nucleosynthesis products. We also report how nucleosynthesis is sensitive to the<br />
variation <strong>of</strong> the initial abundance <strong>of</strong> elements in the accretion disk, namely whether it<br />
is Si rich or He rich. In addition to the formation <strong>of</strong> various isotopes <strong>of</strong> Fe, Co and Ni<br />
we report the synthesis <strong>of</strong> new elements like Ar35, F21, Mn53 and various isotopes <strong>of</strong><br />
Cr which have not been reported earlier. Next, we investigate whether these elements<br />
survive in the outflows from the disk and we find that the result is sensitive to the<br />
fraction <strong>of</strong> mass ejected to the mass accreted and hence to the velocity <strong>of</strong> ejection.<br />
When the velocity <strong>of</strong> ejection is small we find that many new elements like isotopes <strong>of</strong><br />
Ti, V, Cu and Zn are synthesized. We also give a rough estimate <strong>of</strong> the change in the<br />
mass fraction <strong>of</strong> a particular species due to these core collapse events during the<br />
lifetime <strong>of</strong> a galaxy, which affects the metallicity <strong>of</strong> the universe. Many <strong>of</strong> these<br />
elements thus synthesized have been observed in the Xray afterglows <strong>of</strong> several<br />
gammaray bursts.
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