Cooperative Phenomenon of Ferromagnetism and Unconventional Superconductivity in UGe$_2$: A ^73^Ge-NQR Study under Pressure

TL;DR

This study investigates the interplay of ferromagnetism and unconventional superconductivity in UGe₂ under pressure, revealing phase separation and that superconductivity coexists with ferromagnetism but not with paramagnetism.

Contribution

It provides experimental evidence of phase separation and the coexistence of ferromagnetism and superconductivity in UGe₂ using ^73Ge-NQR under pressure, highlighting a first-order transition.

Findings

Phase separation into ferromagnetic and paramagnetic phases near 1.5 GPa.

Superconductivity emerges only within the ferromagnetic phase.

First-order transition indicated by phase separation evidence.

Abstract

We report on a cooperative phenomenon of ferromagnetism and unconventional superconductivity (SC) in UGe$_2$ through the measurements of $^{73}$Ge nuclear-quadrupole-resonance (NQR) under pressure ($P$). The NQR spectra evidenced phase separation into ferromagnetic and paramagnetic phases in the vicinity of $P_c\sim 1.5$ GPa, pointing to a first-order transition. The measurements of nuclear-spin-lattice-relaxation-rate $1/T_1$ revealed that SC emerges under the background of ferromagnetism, but not of the paramagnetic phase.