Flux line lattice melting and the formation of a coherent quasiparticle bloch state in the ultraclean URuSi superconductor

「超純良」超伝導体URuSiの磁束格子融解と準粒子ブロッホ状態

岡崎 竜二*; 笠原 裕一*; 宍戸 寛明*; Konczykowski, M.*; Behnia, K.*; 芳賀 芳範   ; 松田 達磨; 大貫 惇睦; 芝内 孝禎*; 松田 祐司*

Okazaki, Ryuji*; Kasahara, Yuichi*; Shishido, Hiroaki*; Konczykowski, M.*; Behnia, K.*; Haga, Yoshinori; Matsuda, Tatsuma; Onuki, Yoshichika; Shibauchi, Takasada*; Matsuda, Yuji*

We find that in ultraclean heavy-fermion superconductor URuSi ( K) a distinck flux line lattice melting transition with outstanding characters occurs well below the mean-field upper critical fields. We show that a very small number of carriers with heavy mass in this system results in exceptionally large thermal fluctuations even at subkelvin temperatures, which are witnessed by a sizable region of the flux line liquid phase. The uniqueness is further highlighted by an enhancement of the quasiparticle mean free path below the melting transition, implying a possible formation of a quasiparticle Bloch state in the periodic flux line lattice.