Thermal conductivity in a mixed state of a superconductor at low magnetic fields

TL;DR

This paper provides a detailed theoretical analysis of low-field thermal conductivity in s-wave superconductors, revealing that quasiparticle tunneling between vortices limits heat transport and that a second weaker band can significantly enhance thermal conductivity.

Contribution

It introduces a parameter-free analytical solution for single-band superconductors and explores how two-band systems' heat transport depends on gap ratios and diffusion constants.

Findings

Heat transport is limited by quasiparticle tunneling between vortices.

The analytical solution sets a lower limit for heat transport in the mixed state.

Presence of a weaker second band enhances thermal conductivity at low fields.

Abstract

We evaluate accurate low-field/low-temperature asymptotics of the thermal conductivity perpendicular to magnetic field for one-band and two-band s-wave superconductors using Keldysh-Usadel formalism. We show that heat transport in this regime is limited by tunneling of quasiparticles between adjacent vortices across a number of local points and therefore widely-used approximation of averaging over circular unit cell is not valid. In the single-band case, we obtain parameter-free analytical solution which provides theoretical lower limit for heat transport in the mixed state. In the two-band case, we show that heat transport is controlled by the ratio of gaps and diffusion constants in different bands. Presence of a weaker second band strongly enhances the thermal conductivity at low fields