Rotational symmetry breaking in the hidden-order phase of URuSi

URuSiの隠れた秩序相における回転対称性の破れ

岡崎 竜二*; 芝内 孝禎*; Shi, H. J.*; 芳賀 芳範   ; 松田 達磨; 山本 悦嗣  ; 大貫 惇睦; 池田 浩章*; 松田 祐司*

Okazaki, Ryuji*; Shibauchi, Takasada*; Shi, H. J.*; Haga, Yoshinori; Matsuda, Tatsuma; Yamamoto, Etsuji; Onuki, Yoshichika; Ikeda, Hiroaki*; Matsuda, Yuji*

The nature of the broken symmetry in the so-called "hidden order" phase transition in the heavyfermion compound URuSi has posed a long-standing mystery. We report the emergence of an in-plane anisotropy of the magnetic susceptibility below the transition temperature, which breaks the four-fold rotational symmetry of the tetragonal URuSi. Our findings suggest that the hidden order phase is an electronic "nematic" phase, a translationally invariant metallic phase with spontaneous breaking of rotational symmetry.