Anisotropic response of spin susceptibility in the superconducting state of UTe2 probed with Te125−NMR measurement

To investigate spin susceptibility in a superconducting (SC) state, we measured the $^{125}\mathrm{Te}$-NMR Knight shifts at magnetic fields ($H$) up to 6.5 T along the $b$ and $c$ axes of single-crystal ${\mathrm{UTe}}_{2}$, 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 6.5 T. 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 on the $bc$ plane. We discuss the possible $\mathbit{d}$-vector state within the spin-triplet scenario and suggest that the dominant $\mathbit{d}$-vector component for the case of $H\ensuremath{\parallel}b$ changes above 13 T, where ${T}_{\mathrm{c}}$ increases with increasing $H$.