Theory of thermal and charge transport in diffusive normal metal / superconductor junctions

TL;DR

This paper investigates thermal and charge transport in diffusive normal metal/superconductor junctions, deriving new formulas and analyzing how various factors influence conductance, with implications for identifying pairing symmetries.

Contribution

It introduces a general expression for thermal conductance and analyzes the effects of proximity and mid-gap states on transport properties in superconductor junctions.

Findings

Proximity effect does not influence thermal conductance.

Mid-gap Andreev resonant states suppress thermal conductance.

Electrical and thermal conductance dependencies can help distinguish pairing symmetries.

Abstract

Thermal and charge transport in the diffusive normal metal(DN) / insulator / $s$-, $d$- and p-wave superconductor junctions are studied for various situations, where we have used the Usadel equation with Nazarov's generalized boundary condition. Thermal and electrical conductance of the junction and the Lorentz ratio are calculated by varying the magnitudes of the resistance, the Thouless energy and the magnetic scattering rate in DN, the transparency of the insulating barrier, and the angle between the normal to the interface and the crystal axis of d-wave superconductors or the angle between the normal to the interface and the lobe direction of the p-wave pair potential. New general expression is derived for the calculation of the thermal conductance. It is demonstrated that the proximity effect doesn't influence the thermal conductance while the mid gap Andreev resonant states suppress it. We have also discussed a possibility of distinguishing pairing symmetries based on the dependencies of the electrical and thermal conductance on temperatures.