# Spin-triplet superconductivity in the paramagnetic UCoGe under pressure studied by $^{59}$Co NMR

## TL;DR

This study uses $^{59}$Co NMR to investigate spin-triplet superconductivity in UCoGe under pressure, revealing broad spectra in the paramagnetic state consistent with unconventional pairing.

## Contribution

First NMR study of UCoGe in the paramagnetic state under pressure showing evidence for spin-triplet superconductivity.

## Key findings

- Spectra broaden in the superconducting state without significant shift.
- Knight shift change is small, supporting triplet pairing.
- Broadening linked to spin-triplet superconductivity properties.

## Abstract

A $^{59}$Co nuclear magnetic resonance (NMR) measurement was performed on the single-crystalline ferromagnetic (FM) superconductor UCoGe under a pressure of 1.09 GPa, where the FM state is suppressed and superconductivity occurs in the paramagnetic (PM) state, to study the superconducting (SC) state in the PMstate. $^{59}$Co-NMR spectra became broader but hardly shifted across the SC transition temperature. The Knight-shift change determined from fitting the spectral peak with a Gaussian was much smaller than the spin part of the Knight shift; this is in good agreement with the spin-triplet pairing suggested from the large upper critical field. The spectrum broadening in the SC state cannot be attributed to the SC diamagnetic effect but is related to the properties of spin-triplet superconductivity. The origins of the broadening are discussed herein.