Topological properties of ferromagnetic superconductors

TL;DR

This paper explores the topological properties of ferromagnetic superconductors like UCoGe, highlighting how pressure influences their magnetic and superconducting phases, and proposing a model for their phase transitions.

Contribution

It introduces a phenomenological model explaining the coexistence of ferromagnetism and superconductivity and predicts a first-order transition between phases.

Findings

Superconductivity in UCoGe persists across the ferromagnetic quantum critical point.

Spin-orbit interactions stabilize a time-reversal invariant odd-parity superconductor.

The transition from normal to coexistence phase is predicted to be first-order.

Abstract

A variety of heavy fermion superconductors, such as UCoGe, UGe$_2$, and URhGe exhibit a striking coexistence of bulk ferromagnetism and superconductivity. In these systems, the magnetic moment decreases with pressure, and vanishes at a ferromagnetic quantum critical point (qcp). Remarkably, the superconductivity in UCoGe varies smoothly with pressure across the qcp and exists in both the ferromagnetic and paramagnetic regimes. We argue that in UCoGe, spin-orbit interactions stabilize a time-reversal invariant odd-parity superconductor in the high pressure paramagnetic regime. Based on a simple phenomenological model, we predict that the transition from the paramagnetic normal state to the phase where superconductivity and ferromagnetism coexist, is a first-order transition.