Longitudinal spin fluctuations driving field-reinforced superconductivity in UTe

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.*

Our measurements of Te NMR relaxations reveal an enhancement of electronic spin fluctuations above ~T, leading to their divergence in the vicinity of the metamagnetic transition at ~T, below which field-reinforced superconductivity appears when a magnetic field () is applied along the crystallographic axis. The NMR data evidence that these fluctuations are dominantly longitudinal, providing a key to understanding the peculiar superconducting phase diagram in , where such fluctuations enhance the pairing interactions.