Impurity-Induced Quasiparticle Transport and Universal Limit Wiedemann-Franz Violation in d-Wave Superconductors

TL;DR

This paper investigates impurity effects on quasiparticle transport in d-wave superconductors, revealing that thermal conductivity remains universal at low temperatures, unaffected by impurities or Fermi liquid interactions, thus aiding experimental analysis.

Contribution

The study improves previous models by including vertex and Fermi liquid corrections, demonstrating the universality of thermal conductivity in the presence of impurities.

Findings

Thermal conductivity remains universal despite impurities.

Electrical conductivity is affected by vertex corrections.

Fermi liquid interactions influence electrical and spin conductivities.

Abstract

Due to the node structure of the gap in a d-wave superconductor, the presence of impurities generates a finite density of quasiparticle excitations at zero temperature. Since these impurity-induced quasiparticles are both generated and scattered by impurities, prior calculations indicate a universal limit (\Omega -> 0, T -> 0) where the transport coefficients obtain scattering-independent values, depending only on the velocity anisotropy v_f/v_2. We improve upon prior results, including the contributions of vertex corrections and Fermi liquid corrections in our calculations of universal limit electrical, thermal, and spin conductivity. We find that while vertex corrections modify electrical conductivity and Fermi liquid corrections renormalize both electrical and spin conductivity, only thermal conductivity maintains its universal value, independent of impurity scattering or Fermi liquid interactions. Hence, low temperature thermal conductivity measurements provide the most direct means of obtaining the velocity anisotropy for high T_c cuprate superconductors.