Unconventional superconductors under rotating magnetic field II: thermal transport

TL;DR

This paper develops a microscopic theoretical framework to calculate thermal conductivity in unconventional superconductors under rotating magnetic fields, aiding the interpretation of experimental gap structure measurements.

Contribution

It introduces a quasiclassical approach using the Keldysh formulation and an adapted BPT method to analyze thermal transport in superconductors with complex Fermi surfaces.

Findings

Identifies the dependence of thermal conductivity on magnetic field direction relative to gap nodes.

Establishes the location of gap nodes in CeCoIn5 and κ-(BEDT-TTF)2Cu(NCS)2 based on anisotropy analysis.

Provides a theoretical basis for interpreting experimental thermal transport data in unconventional superconductors.

Abstract

We present a microscopic approach to the calculations of thermal conductivity in unconventional superconductors for a wide range of temperatures and magnetic fields. Our work employs the non-equilibrium Keldysh formulation of the quasiclassical theory. We solve the transport equations using a variation of the Brandt-Pesch-Tewordt (BPT) method, that accounts for the quasiparticle scattering on vortices. We focus on the dependence of the thermal conductivity on the direction of the field with the respect to the nodes of the order parameter, and discuss it in the context of experiments aiming to determine the shape of the gap from such anisotropy measurements. We consider quasi-two dimensional Fermi surfaces with vertical line nodes and use our analysis to establish the location of gap nodes in heavy fermion CeCoIn$_5$ and organic superconductor $\kappa$-(BEDT-TTF)$_2$Cu(NCS)$_2$.