Low magnetic field phase diagram of UCoGe

TL;DR

This paper presents a phase diagram of UCoGe showing superconductivity coexists with ferromagnetic fluctuations at ambient pressure, with superconductivity persisting without long-range ferromagnetic order and dominating in small magnetic fields.

Contribution

It provides new experimental evidence that superconductivity exists without long-range ferromagnetic order in UCoGe at ambient pressure, based on neutron polarimetry and other measurements.

Findings

Superconductivity exists without long-range ferromagnetic order.

Superconductivity dominates over paramagnetic state in small magnetic fields.

The zero-field state shows strong ferromagnetic spin fluctuations.

Abstract

We propose an alternate scenario for the relation between ferromagnetism (FM) and superconductivity (SC) in UCoGe at ambient pressure. On the basis of neutron polarimetry measurement performed in strictly zero field on a single-crystal at ambient pressure, we claim that the SC phase does exist in spite of lack of long-range FM order. Moreover, the SC regime dominates to the paramagnetic (PM) state in small external magnetic fields. Above the critical SC temperature, TSC = 0.64 K, the zero-field state is characterized by a regime with strong FM spin fluctuations, suggesting the proximity of the FM quantum critical point. We present an ambient-pressure phase diagram of UCoGe based on our resistivity, magnetization and neutron polarimetry results.