Upper critical field of p-wave ferromagnetic superconductors with orthorhombic symmetry

TL;DR

This paper extends the Scharnberg-Klemm theory to orthorhombic p-wave ferromagnetic superconductors, explaining complex upper critical field behaviors observed in UCoGe under strong magnetic fields.

Contribution

It introduces a generalized model for $H_{c2}(T)$ in orthorhombic p-wave superconductors with partial symmetry breaking, applicable to ferromagnetic materials like UCoGe.

Findings

The model reproduces upward curvature in $H_{c2}(T)$ for all crystal axes.

Good fits to experimental data of UCoGe are achieved.

The theory explains complex anisotropic critical field behaviors.

Abstract

We extended the Scharnberg-Klemm theory of $H_{c2}(T)$ in p-wave superconductors with broken symmetry to cases of partially broken symmetry in an orthorhombic crystal, as is appropriate for the more exotic ferromagnetic superconductor UCoGe in strong magnetic fields. For some partially broken symmetry cases, $H_{c2}(T)$ can mimic upward curvature in all three crystal axis directions, and reasonably good fits to some of the UCoGe data are obtained.