Phase diagram of UCoGe

TL;DR

This paper develops a Landau theory to describe the complex phase diagram of UCoGe, a ferromagnetic superconductor, detailing four phase transitions and their magnetic and superconducting properties.

Contribution

It provides a theoretical framework for understanding the sequence of phase transitions and the emergence of screening currents in UCoGe's phase diagram.

Findings

Identification of four distinct phase transitions.

Distinct magnetic behaviors at different transitions.

Theoretical prediction of screening currents during transitions.

Abstract

The temperature-pressure phase diagram of ferromagnetic superconductor UCoGe includes four phase transitions. They are between the paramagnetic and the ferromagnetic states with the subsequent transition in the superconducting ferromagnetic state and between the normal and the superconducting states after which has to occur the transition to the superconducting ferromagnetic state. Here we have developed the Landau theory description of the phase diagram and established the specific ordering arising at each type of transition. The phase transitions to the ferromagnetic superconducting state are inevitably accompanied by the emergency of screening currents. The corresponding magnetostatics considerations allow to establish the significant difference between the transition from the ferromagnetic to the ferromagnetic superconducting state and the transition from the superconducting to the ferromagnetic superconducting state.