Absence of the Pauli-Paramagnetic Limit in a Superconducting U6Co

Masahiro Manago,Kenji Ishida,Dai Aoki

doi:10.7566/jpsj.86.073701

Abstract

We performed $^{59}$Co nuclear magnetic resonance (NMR) measurements of single-crystalline U$_6$Co. There is a small decrease in the Knight shift in the superconducting (SC) state, but this change mainly arises from the SC diamagnetic effect. The negligible change of the spin part of the Knight shift, together with the absence of the Pauli-paramagnetic effect in the SC U$_6$Co, is understood as a consequence of the small spin susceptibility. The nuclear spin-lattice relaxation rate $1/T_1$ is also measured in the SC state under the magnetic field, and exhibits a tiny Hebel-Slichter peak just below the SC transition temperature and exponential behavior at lower temperatures. These behaviors are in agreement with the full-gap s-wave pairing in U$_6$Co.

Highlights

We performed 59Co nuclear magnetic resonance (NMR) measurements of single-crystalline U6Co
This is because the spin susceptibility decreases in the SC state, and the energy difference between the SC and the normal states reduces under a larger magnetic field due to the magnetic energy in the normal state
We report 59Co NMR measurements of U6Co, which are performed to further investigate the electronic spin susceptibility from a microscopic point of view

Summary

Introduction

We performed 59Co nuclear magnetic resonance (NMR) measurements of single-crystalline U6Co. We adopt κ = 86 for the best fit of the experiment, which is close to κ 70 estimated from Hc2 and the thermodynamic field.[6] This suggests that the diamagnetic effect is a dominant origin of the Knight-shift change in U6Co. The magnitude of Ks could not be properly determined in this study, but there is a constraint on the value of Ks, as discussed below.

Results

Conclusion