Superconducting order parameter in UTe determined by knight shift measurement

Fujibayashi, Hiroki*; Nakamine, Genki*; Kinjo, Katsuki*; Kitagawa, Shunsaku*; Ishida, Kenji*; Tokunaga, Yo  ; Sakai, Hironori   ; Kambe, Shinsaku  ; Nakamura, Ai*; Shimizu, Yusei*; Homma, Yoshiya*; Li, D.*; Honda, Fuminori*; Aoki, Dai*

This study investigates the spin susceptibility in U-based superconductor UTe in the superconducting (SC) state by using Knight shift measurements for a magnetic field along the axis, which is the magnetic easy axis of UTe. Although a tiny anomaly ascribed to the SC diamagnetic effect was observed just below the SC transition temperature , the -axis Knight shift in the SC state shows no significant decrease, following the extrapolation from the normal-state temperature dependence. This indicates that the spin susceptibility is nearly unchanged below . Considering the previous Knight shift results for and , the dominant SC state is determined to be in the spin-triplet pairing, which is consistent with the spin anisotropy in the normal state. The present result shows that UTe is a spin-triplet superconductor with spin degrees of freedom.