Enhancement of superconductivity near the ferromagnetic quantum critical point in UCoGe

TL;DR

This study investigates how superconductivity in UCoGe is enhanced near a ferromagnetic quantum critical point, showing that superconductivity peaks as ferromagnetism vanishes under pressure, indicating a close link between the two phenomena.

Contribution

The paper provides the first detailed high-pressure phase diagram of UCoGe, demonstrating the enhancement of superconductivity near the ferromagnetic quantum critical point and evidence for spin-triplet pairing.

Findings

Ferromagnetism vanishes at 1.4 GPa under pressure.

Superconductivity is enhanced near the critical pressure.

Large upper-critical fields suggest spin-triplet pairing.

Abstract

We report a high-pressure single crystal study of the superconducting ferromagnet UCoGe. Ac-susceptibility and resistivity measurements under pressures up to 2.2 GPa show ferromagnetism is smoothly depressed and vanishes at a critical pressure $p_c = 1.4$ GPa. Near the ferromagnetic critical point superconductivity is enhanced. Upper-critical field measurements under pressure show $B_{c2}(0)$ attains remarkably large values, which provides solid evidence for spin-triplet superconductivity over the whole pressure range. The obtained $p-T$ phase diagram reveals superconductivity is closely connected to a ferromagnetic quantum critical point hidden under the superconducting `dome'.