Self-reconstruction of order parameter in spin-triplet superconductor UTe

Tokiwa, Yoshifumi  ; Opletal, P.  ; Sakai, Hironori   ; Kubo, Katsunori ; Kambe, Shinsaku  ; Yamamoto, Etsuji  ; Kimata, Motoi; Awaji, Satoshi*; Sasaki, Takahiko*; Aoki, Dai*; Yanase, Yoichi*; Tokunaga, Yo  ; Haga, Yoshinori   

We investigate the effect of easy-axis metamagnetic crossover on superconductivity in UTe along the -axis through measurements of AC susceptibility, magnetization, and the magnetocaloric effect. In ultra-clean single crystals, we identify a field-induced phase transition within the superconducting state at 5.6 T, driven by metamagnetism. This transition leads to a high-field superconducting state, significantly increasing the upper critical field to 12 T. A sudden increase in entropy at the transition suggests a self-reconstruction of the order parameter, enabling multi-component superconducting states to adapt to external perturbations.