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

Abstract

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.