Superconducting Properties of Heavy Fermion UTe₂ Revealed by ¹²⁵Te-nuclear Magnetic Resonance

Abstract

We have performed the ¹²⁵Te-nuclear magnetic resonance (NMR) measurement in the field along the b axis on the newly discovered superconductor UTe₂, which is a candidate of a spin-triplet superconductor. The nuclear spin–lattice relaxation rate divided by temperature 1/T₁T abruptly decreases below a superconducting (SC) transition temperature Tc without showing a coherence peak, indicative of UTe₂ being an unconventional superconductor. It was found that the temperature dependence of 1/T₁T in the SC state cannot be understood by a single SC gap behavior but can be explained by a two SC gap model. The Knight shift, proportional to the spin susceptibility, decreases below Tc, but the magnitude of the decrease is much smaller than the decrease expected in the spin-singlet pairing. Rather, the small Knight-shift decrease as well as the absence of the Pauli-depairing effect can be interpreted by the spin triplet scenario.