Finite Density of States in a Mixed State of d_x^2-y^2+id_xy Superconductor

TL;DR

This paper calculates the quasiparticle density of states in a mixed d_x^2-y^2+id_xy superconductor, showing it remains gapless in a magnetic field and matches experimental thermal conductivity data, while analyzing disorder effects and field crossover behaviors.

Contribution

It provides a detailed analysis of the density of states and thermal conductivity in a mixed superconductor, including disorder effects and field crossover phenomena.

Findings

Quasiparticle spectrum remains gapless due to Doppler shift.

Thermal conductivity scales as √H with field, matching experiments.

Disorder effects and H log H crossover are significant at small fields.

Abstract

We have calculated the density of states of quasiparticles in a d_x^2-y^2+id_xy superconductor, and show that in the mixed state the quasiparticle spectrum remains gapless because of the Doppler shift by superflow. It was found that if the d_{xy} order gap $\Delta_1\propto \sqrt{H}$ as suggested by experiments, then thermal conductivity $\kappa \propto \sqrt{H}$ in accord with experimental data at lowest temperatures. This is an appended version of the paper published in Phys. Rev. {\bf B 59}, 6024, (1999). We now also discuss the disorder effects and analyze the H log H crossover at small fields. We argue that H log H regime is present and disorder effect is dominant as the field-induced seconary gap is small at small fields.