Nodal structure of quasi-2D superconductors probed by magnetic field

TL;DR

This paper investigates how the specific heat and heat conductivity in quasi-2D superconductors with line nodes depend on magnetic field orientation, revealing signatures of the nodal structure and clarifying the gap symmetry in CeCoIn$_5$.

Contribution

It introduces a microscopic method to analyze quasiparticle scattering in vortex states, providing new insights into the nodal structure through anisotropic thermodynamic measurements.

Findings

Specific heat anisotropy changes sign with temperature at moderate fields.

Analysis supports a $d_{x^2-y^2}$ gap symmetry in CeCoIn$_5$.

Method effectively distinguishes nodal structures in superconductors.

Abstract

We consider a quasi two-dimensional superconductor with line nodes in an in-plane magnetic field, and compute the dependence of the specific heat, $C$, and the in-plane heat conductivity, $\kappa$, on the angle between the field and the nodal direction in the vortex state. We use a variation of the microscopic Brandt-Pesch-Tewordt method that accounts for the scattering of quasiparticles off vortices, and analyze the signature of the nodes in $C$ and $\kappa$. At low to moderate fields the specific heat anisotropy changes sign with increasing temperature. Comparison with measurements of $C$ and $\kappa$ in CeCoIn$_5$ resolves the contradiction between the two in favor of the $d_{x^2-y^2}$ gap.