Spin susceptibility in the superconducting state of UTe₂ probed with ¹²⁵Te-NMR

To investigate spin susceptibility in a superconducting (SC) state, we measured the ¹²⁵Te-nuclear magnetic resonance (NMR) Knight shifts at magnetic fields (H) 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 K_c, respectively) decreased slightly and the decrease in K_b was almost constant up to 7T. The reduction in K_c decreased with increasing H, and K_c 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 T_c increases with increasing H.