Anisotropic response of spin susceptibility in the superconducting state of UTe$_2$ probed with $^{125}$Te-NMR measurement

Abstract

To investigate spin susceptibility in a superconducting (SC) state, we measured the 125 Te-nuclear magnetic resonance (NMR) Knight shifts at magnetic fields (H) up to 6.5 T along the b and c axes of single-crystal UTe2, a promising candidate for a spin-triplet superconductor. In the SC state, the Knight shifts along the b and c axes (K b and Kc, respectively) decreased slightly and the decrease in K b was almost constant up to 6.5 T. The reduction in Kc decreased with increasing H, and Kc was unchanged through the SC transition temperature at 5.5 T, excluding the possibility of spin-singlet pairing. Our results indicate that spin susceptibilities along the b and c axes slightly decrease in the SC state in low H, and the H response of SC spin susceptibility is anisotropic in the bc plane. We discuss the possible d-vector state within the spin-triplet scenario and suggest that the dominant d-vector component for the case of H b changes above 13 T, where Tc increases with increasing H.

Magnetic Properties under Pressure in Novel Spin-Triplet Superconductor UTe2

“…Strongest evidence for spintriplet superconductivity in UTe 2 was given by the Knight * aoki@imr.tohoku.ac.jp shift of NMR experiments, which shows only a tiny decrease of the spin susceptibility below T c . 15,16) Another important point in UTe 2 is the appearance of multiple superconducting phases under pressure. 17) The superconducting transition at T c splits into two above 0.25 GPa.…”