Phonon drag and carrier diffusion contribution to heat transport of superconductor MgB2

2017 ◽  
Vol 06 (01) ◽  
pp. 1750008 ◽  
Author(s):  
Roopam Sharma ◽  
Namita Singh ◽  
Khurshid Akhtar ◽  
R. Khenata ◽  
Dinesh Varshney
Keyword(s):  
Heat Transfer ◽  
Relaxation Time ◽  
Thermoelectric Power ◽  
Linear Temperature Dependence ◽  
Phonon Drag ◽  
Scattering Mechanism ◽  
Linear Temperature ◽  
Carrier Diffusion ◽  
Time Approximation ◽  
Relaxation Time Approximation

The temperature variation of phonon drag thermoelectric power [Formula: see text] is computed within the relaxation time approximation for high temperature MgB2 superconductors. The phonon drag thermoelectric power ([Formula: see text] in normal state of MgB2 superconductors dominates and is an artifact of strong phonon-impurity and phonon scattering mechanism. The carrier diffusive thermoelectric power is explored when heat transfer is limited by the scattering of phonons from defects, grain boundaries, phonons and charge carriers. The carrier diffusion contribution to the thermoelectric power ([Formula: see text] is analyzed keeping in mind the inherent two energy gaps. The conductivity within the relaxation time approximation for [Formula: see text] and [Formula: see text] band carriers has been taken into account ignoring a possible energy dependence of the scattering rates. Such an estimate sets an upperbound on [Formula: see text] and is about 50% of total heat transfer at room temperature. Both these channels for heat transfer are added and [Formula: see text] starts departing from linear temperature dependence at about 150[Formula: see text]K, before increasing at higher temperatures weakly. It is shown that the behavior of the [Formula: see text] is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance between carrier diffusion and phonon drag contributions. The numerical analysis of thermoelectric power in the metallic phase of MgB2 shows similar results as those revealed from experiments. The anomalies reported experimentally are well accounted in terms of the scattering mechanism by phonon drag and carrier scattering with impurities.

PHONON DRAG AND CARRIER DIFFUSION CONTRIBUTIONS IN THERMOELECTRIC POWER OF K3C60 FULLERIDES

2012 ◽  
Vol 01 (03) ◽  
pp. 1250027 ◽  
Author(s):  
DINESH VARSHNEY ◽  
RAJENDRA JAIN ◽  
NAMITA SINGH
Keyword(s):  
Relaxation Time ◽  
Thermoelectric Power ◽  
Phonon Scattering ◽  
Linear Temperature Dependence ◽  
Phonon Drag ◽  
Linear Temperature ◽  
Carrier Diffusion ◽  
Time Approximation ◽  
Relaxation Time Approximation ◽  
Heat Carriers

The thermoelectric power (S) of K3C60 fullerides is theoretically analyzed. Mott expression within parabolic band approximation is used to reveal the electron diffusive thermoelectric power (Sc diff ) following Fermi energy as electron parameter, Sc diff show linear temperature dependence. S infers a change in slope above transition temperature and become almost linear above 70 K. The phonon drag thermoelectric power (S ph drag ) is computed within relaxation time approximation when thermoelectric power is limited by scattering of phonons from defects, grain boundaries, phonons and electrons as carriers. The S ph drag of K3C60 is anomalous and it is an artifact of strong phonon-electron and phonon scattering mechanism. The thermoelectric power within relaxation time approximation has been taken into account ignoring a possible energy dependence of the scattering rates. Behaviour of S(T) is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance between carrier diffusion and phonon drag contributions.

PHONON DRAG, CARRIER DIFFUSIVE THERMOELECTRIC POWER AND SEMICONDUCTING RESISTIVITY BEHAVIOR OF Zn NANOWIRES

2010 ◽  
Vol 09 (05) ◽  
pp. 453-459
Author(s):  
K. K. CHOUDHARY ◽  
D. PRASAD ◽  
K. JAYAKUMAR ◽  
DINESH VARSHNEY
Keyword(s):  
Grain Boundaries ◽  
Thermoelectric Power ◽  
Charge Carriers ◽  
Fourth Power ◽  
Linear Temperature Dependence ◽  
Phonon Drag ◽  
Acoustic Phonons ◽  
Temperature Dependent ◽  
Linear Temperature ◽  
Model Hamiltonian

In this paper, we undertake a quantitative analysis of observed temperature-dependent thermoelectric power (S) of 4 nm Zn /Vycor composite nanowires by developing a model Hamiltonian that incorporates scattering of acoustic phonons with impurities, grain boundaries, charge carriers and phonons. Mott expression is used to determine the carrier diffusive thermoelectric power [Formula: see text]. The [Formula: see text] shows linear temperature dependence and the computed [Formula: see text] when subtracted from the experimental data is interpreted as phonon drag thermoelectric power [Formula: see text]. The model Hamiltonian within the relaxation time approximation sets the limitations of the scattering of acoustic phonons with impurities, grain boundaries, charge carriers and phonons for thermoelectric power in the nanowires. It is shown that for acoustic phonons the scattering and transport cross sections are proportional to fourth power of the phonon in the Rayleigh regime. The resultant thermoelectric powers is an artefact of various operating scattering mechanisms and are computed for the first time to our knowledge for Zn nanowires consistent with the experimentally reported behavior. The semiconducting nature of resistivity is discussed with small polaron conduction (SPC) model which consistently retraces the temperature-dependent resistivity behavior of Zn /Vycor composite.

scholarly journals Bulk viscosity of strongly interacting matter in the relaxation time approximation

2018 ◽  
Vol 97 (4) ◽  
Author(s):  
Alina Czajka ◽  
Sigtryggur Hauksson ◽  
Chun Shen ◽  
Sangyong Jeon ◽  
Charles Gale
Keyword(s):  
Relaxation Time ◽  
Bulk Viscosity ◽  
Time Approximation ◽  
Relaxation Time Approximation ◽  
Strongly Interacting

scholarly journals Calculations of the thermal conductivity of Si1-xGex films with nonuniform composition

2018 ◽  
Vol 19 (1) ◽  
pp. 48-52
Author(s):  
V. V. Kuryliuk ◽  
O. M. Krit
Keyword(s):  
Thermal Conductivity ◽  
Relaxation Time ◽  
Boltzmann Equation ◽  
Temperature Interval ◽  
Thermoelectric Properties ◽  
Bulk Material ◽  
Nonuniform Distribution ◽  
Time Approximation ◽  
Relaxation Time Approximation ◽  
Available Information

SiGe films have attracted much attention recently due to experimental demonstrations of improved thermoelectric properties over those of the corresponding bulk material. However, despite this increasing attention, available information on the thermoelectric properties of Si1-xGex films is quite limited, especially for nonuniform composition in wide temperature interval. In this paper we have used the Boltzmann equation under the relaxation-time approximation to calculate the thermal conductivity of Si1-xGex films with nonuniform composition. It is confirmed that SiGe films with nonuniform composition has significantly lower thermal conductivity than its uniform counterpart. This suggests that an improvement in thermoelectric properties is possible by using the SiGe films with nonuniform distribution of germanium.

Longitudinal magnetoresistance in silver and copper between 4.2 and 35 °K

1967 ◽  
Vol 302 (1468) ◽  
pp. 83-98 ◽  
Keyword(s):  
Relaxation Time ◽  
Electron Scattering ◽  
Small Angle ◽  
Time Approximation ◽  
Long Wavelength ◽  
Relaxation Time Approximation ◽  
Angle Scattering ◽  
Different Types ◽  
Pure Single Crystal ◽  
Longitudinal Magnetoresistance

Longitudinal magnetoresistance has been measured in a number of single crystals of silver and one very pure single crystal of copper in fields up to 65 kG and at temperatures between 4.2 and 35 °K. The purpose of the work has been to investigate the effects of different types of electron scattering, in particular small angle scattering. It has been found that at 4.2 °K impure crystals obey the relaxation time approximation fairly well, whereas crystals that have been purified (by oxidation at 800 °C) do not. Above 4.2 °K, the addition of long wavelength phonons has caused the magnetoresistance to increase substantially, as predicted by Pippard (1964), but agreement with Pippard’s theory is only qualitative. To account for the results a more detailed treatment of the scattering is required.

LATTICE THERMAL CONDUCTIVITY IN A HOLLOW SILICON NANOWIRE

2005 ◽  
Vol 19 (06) ◽  
pp. 1017-1027 ◽  
Author(s):  
WEI-QING HUANG ◽  
KE-QIU CHEN ◽  
Z. SHUAI ◽  
LINGLING WANG ◽  
WANGYU HU
Keyword(s):  
Thermal Conductivity ◽  
Relaxation Time ◽  
Lattice Thermal Conductivity ◽  
Silicon Nanowire ◽  
Boundary Scattering ◽  
Phonon Confinement ◽  
Time Approximation ◽  
Si Nanowire ◽  
Scattering Mechanisms ◽  
Relaxation Time Approximation

We theoretically investigate the lattice thermal conductivity of a hollow Si nanowire under the relaxation time approximation. The results show that the thermal conductivity in such structure is decreased markedly below the bulk value due to phonon confinement and boundary scattering. The thermal conductivities under different scattering mechanisms are given, and it is found that the boundary scattering is dominant resistive process for the decrease of the thermal conductivity.

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