High-field NMR study of spin fluctuations and field-reinforced superconductivity in UTe

UTeにおけるスピン揺らぎと磁場強化型超伝導の強磁場NMRによる研究

徳永 陽  ; 酒井 宏典   ; 神戸 振作  ; Opletal, P.  ; 常盤 欣文  ; 芳賀 芳範   ; 北川 俊作*; 石田 憲二*; 青木 大*; Knebel, G.*; Lapertot, G.*; Krmer, S.*; Horvati, M.*

Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Opletal, P.; Tokiwa, Yoshifumi; Haga, Yoshinori; Kitagawa, Shunsaku*; Ishida, Kenji*; Aoki, Dai*; Knebel, G.*; Lapertot, G.*; Krmer, S.*; Horvati, M.*

In this study, to elucidate the nature of spin fluctuations in UTe, we conducted high-field Te NMR experiments in H//b. For the experiment, we prepared Te-enriched single crystals with T =2.0 K using the molten salt flux method discovered recently by ourselves. Our measurements of Te NMR relaxations reveal an enhancement of electronic spin fluctuations above 15 T, leading to their divergence in the vicinity of the metamagnetic transition at 35 T. The NMR data evidence that these fluctuations are dominantly longitudinal, providing a key to understanding the peculiar superconducting phase diagram in H//b, where such fluctuations enhance the pairing interactions. Our NMR experiments also demonstrate the development of longitudinal fluctuations underlying unconventional transport and thermal behaviors in H//b.