Paramagnetic limit of spin-triplet superconductors

TL;DR

This paper investigates the phase diagram of spin-triplet superconductors under magnetic fields, revealing divergence of the paramagnetic limit at low temperatures and complex phase transitions, including first order transitions and tricritical points.

Contribution

It provides a theoretical analysis of the paramagnetic limit and phase transitions in spin-triplet superconductors considering magnetic field effects and symmetry constraints.

Findings

Paramagnetic limit diverges at low temperatures for various field orientations.

First order transitions occur between normal and superconducting phases.

Multiple tricritical points can lead to complex phase transition behavior.

Abstract

We study the phase diagram of spin-triplet superconductors, considering the effect of the external magnetic field on the electrons' spins. For a given symmetry of the order parameter and a generic orientation of the field, we find that the paramagnetic limit for superconductivity diverges at low temperatures. Furthermore, we identify a range of temperatures where the transition between normal and superconducting phases becomes of the first order. When two tricritical points exist along the transition line, a first order phase transition between two superconducting phases may develop in vicinity of the tricritical point with lower temperature. We discuss the implications of our findings for the anisotropy of the upper critical field in UPt$_3$, a candidate material for triplet superconductivity, when both the paramagnetic and orbital effects are taken into account.