Quasiparticles in the Vortex State of Dirty d-Wave Superconductors

TL;DR

This paper investigates how quasiparticles influence the thermal and transport properties of dirty d-wave superconductors in a magnetic field, revealing a crossover in behavior that explains experimental discrepancies.

Contribution

It demonstrates that extended quasiparticle states dominate in the dirty limit and introduces a new H log H behavior at low fields, extending Volovik's clean limit results.

Findings

Extended states dominate in dirty d-wave superconductors.

Identifies a crossover to H log H behavior at low fields.

Explains discrepancies in specific heat measurements.

Abstract

We consider the problem of the vortex contribution to thermal properties of dirty d-wave superconductors. In the clean limit, Volovik has argued that the main contribution to the density of states in a d-wave superconductor arises from extended quasiparticle states which may be treated semiclassically, giving rise to a specific heat contribution \delta C(H)\ltsim H^{1/2} . We show that the extended states continue to dominate the dirty limit, but lead to a H \log H behavior at the lowest fields, H_{c1}\ll H\ll H_{c2}. This crossover may explain recent discrepancies in specicific heat measurements at low temperatures and fields in the cuprate superconductors. We further discuss the field dependence of transport properties within the same model.