title: Cyclotron resonance in the hidden-order phase of URu2Si2.
abstract: We report the first observation of cyclotron resonance in the hidden-order phase of ultraclean URu2Si2 crystals, which allows the full determination of angle-dependent electron-mass structure of the main Fermi-surface sheets. We find an anomalous splitting of the sharpest resonance line under in-plane magnetic-field rotation. This is most naturally explained by the domain formation, which breaks the fourfold rotational symmetry of the underlying tetragonal lattice. The results reveal the emergence of an in-plane mass anisotropy with hot spots along the [110] direction, which can account for the anisotropic in-plane magnetic susceptibility reported recently. This is consistent with the "nematic" Fermi liquid state, in which itinerant electrons have unidirectional correlations.
authors.affiliation: Department of Physics, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Tonegawa
authors.forename: K
authors.initials: K
authors.lastname: Hashimoto
authors.forename: K
authors.initials: K
authors.lastname: Ikada
authors.forename: Y-H
authors.initials: YH
authors.lastname: Lin
authors.forename: H
authors.initials: H
authors.lastname: Shishido
authors.forename: Y
authors.initials: Y
authors.lastname: Haga
authors.forename: T D
authors.initials: TD
authors.lastname: Matsuda
authors.forename: E
authors.initials: E
authors.lastname: Yamamoto
authors.forename: Y
authors.initials: Y
authors.lastname: Onuki
authors.forename: H
authors.initials: H
authors.lastname: Ikeda
authors.forename: Y
authors.initials: Y
authors.lastname: Matsuda
authors.forename: T
authors.initials: T
authors.lastname: Shibauchi