Intrinsic Mechanism for Magneto-Thermal Conductivity Oscillations in Spin-Orbit-Coupled Nodal Superconductors

TL;DR

This paper proposes a mechanism where spin-orbit coupling causes oscillations in thermal conductivity with magnetic field angle in layered nodal superconductors, especially in cuprates like YBa2Cu3O6+x, offering a bulk probe of spin-orbit effects.

Contribution

It introduces a spin-orbit mechanism for magneto-thermal oscillations in nodal superconductors, highlighting its dominance over vortex effects in certain anisotropic materials.

Findings

Spin-orbit coupling induces detectable thermal conductivity oscillations.

In cuprates, the spin-orbit contribution exceeds vortex effects in underdoped samples.

The mechanism provides a bulk method to probe spin-orbit physics in superconductors.

Abstract

We describe a mechanism by which the longitudinal thermal conductivity $\kappa_{xx}$, measured in an in-plane magnetic field, oscillates as a function of field angle in layered nodal superconductors. These oscillations occur when the spin-orbit splitting at the nodes is larger than the nodal scattering rate, and are complementary to vortex-induced oscillations identified previously. In sufficiently anisotropic materials, the spin-orbit mechanism may be dominant. As a particular application, we focus on the cuprate high-temperature superconductor YBa$_2$Cu$_3$O$_{6+x}$. This material belongs to the class of Rashba bilayers, in which individual CuO$_2$ layers lack inversion symmetry although the crystal itself is globally centrosymmetric. We show that spin-orbit coupling endows $\kappa_{xx}/T$ with a characteristic dependence on magnetic field angle that should be easily detected experimentally, and argue that for underdoped samples the spin-orbit contribution is larger than the vortex contribution. A key advantage of the magneto-thermal conductivity is that it is a bulk probe of spin-orbit physics, and therefore not sensitive to inversion breaking at surfaces.