Superconductivity on the border of weak itinerant ferromagnetism in UCoGe

TL;DR

This paper reports the coexistence of ferromagnetism and superconductivity in UCoGe at ambient pressure, highlighting its weak ferromagnetic nature and evidence for triplet pairing mediated by ferromagnetic fluctuations.

Contribution

It provides experimental evidence for bulk ferromagnetism and superconductivity coexistence in UCoGe, emphasizing the role of ferromagnetic fluctuations in mediating triplet superconductivity.

Findings

UCoGe is a weak ferromagnet with T_C=3 K and small magnetic moment.

Superconductivity appears at T_s=0.8 K, coexisting with ferromagnetism.

Evidence suggests triplet superconductivity mediated by ferromagnetic fluctuations.

Abstract

We report the coexistence of ferromagnetic order and superconductivity in UCoGe at ambient pressure. Magnetization measurements show that UCoGe is a weak ferromagnet with a Curie temperature T_{C}= 3 K and a small ordered moment $m_{0}$= 0.03 $\mu_B$. Superconductivity is observed with a resistive transition temperature T_{s} = 0.8 K for the best sample. Thermal-expansion and specific-heat measurements provide solid evidence for bulk magnetism and superconductivity. The proximity to a ferromagnetic instability, the defect sensitivity of T_{s}, and the absence of Pauli limiting, suggest triplet superconductivity mediated by critical ferromagnetic fluctuations.