Change of superconducting character in UTe induced by magnetic field

金城 克樹*; 藤林 裕己*; 北川 俊作*; 石田 憲二*; 徳永 陽  ; 酒井 宏典   ; 神戸 振作  ; 仲村 愛*; 清水 悠晴*; 本間 佳哉*; Li, D. X.*; 本多 史憲*; 青木 大*; 開 康一*; 木俣 基*; 佐々木 孝彦*

Kinjo, Katsuki*; Fujibayashi, Hiroki*; Kitagawa, Shunsaku*; Ishida, Kenji*; Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Nakamura, Ai*; Shimizu, Yusei*; Homma, Yoshiya*; Li, D. X.*; Honda, Fuminori*; Aoki, Dai*; Hiraki, Koichi*; Kimata, Motoi*; Sasaki, Takahiko*

UTe is a recently discovered spin-triplet superconductor. One of the characteristic features of UTe is a magnetic field ()-boosted superconductivity above 16 T when H is applied exactly parallel to the axis. To date, this superconducting (SC) state has not been thoroughly investigated, and the SC properties as well as the spin state of this high- SC (HHSC) phase are not well understood. In this letter, we performed AC magnetic susceptibility and nuclear magnetic resonance measurements and found that, up to 24.8 T, the HHSC state has bulk nature and is quite sensitive to the angle and that its SC character is different from that in the low- SC (LHSC) state. The dominant spin component of the spin-triplet pair is along the axis in the LHSC state but is changed in the HHSC state along the axis. Our results indicate that -induced multiple SC states originate from the remaining spin degrees of freedom.