Spin susceptibility of superconductors with strong spin-orbit coupling

TL;DR

This paper investigates how strong spin-orbit coupling and crystal symmetry affect the anisotropy of Zeeman coupling and the resulting temperature dependence of spin susceptibility in superconductors, revealing significant modifications to low-temperature behavior.

Contribution

It demonstrates that in certain trigonal and hexagonal crystals, the Zeeman coupling vanishes along symmetry axes, altering the expected temperature dependence of spin susceptibility in superconductors.

Findings

Zeeman coupling is strongly anisotropic and vanishes along symmetry axes.

The temperature dependence of spin susceptibility is qualitatively changed.

Low-temperature power-law exponents are significantly modified.

Abstract

We show that in some trigonal and hexagonal crystals the Zeeman coupling of band electrons with an external magnetic field is strongly anisotropic and necessarily vanishes along the main symmetry axis. This leads to qualitative changes in the temperature dependence of the electron spin susceptibility in the superconducting state. In particular, the power-law exponents at low temperatures due to the contribution of the nodal quasiparticles are considerably modified compared to their textbook values.