title: Field-orientation dependence of low-energy quasiparticle excitations in the heavy-electron superconductor UBe(13).
abstract: Low-energy quasiparticle excitations in the superconducting (SC) state of UBe_{13} were studied by means of specific-heat (C) measurements in a rotating field. Quite unexpectedly, the magnetic-field dependence of C(H) is linear in H with no angular dependence at low fields in the SC state, implying that the gap is fully open over the Fermi surfaces, in stark contrast to previous expectations. In addition, a characteristic cubic anisotropy of C(H) was observed above 2 T with a maximum (minimum) for H∥[001] ([111]) within the (11[over ¯]0) plane, in the normal as well as in the SC states. This oscillation possibly originates from the anisotropic response of the heavy quasiparticle bands, and might be a key to understand the unusual properties of UBe_{13}.
authors.affiliation: Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Yusei
authors.initials: Y
authors.lastname: Shimizu
authors.affiliation: Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Shunichiro
authors.initials: S
authors.lastname: Kittaka
authors.affiliation: Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Toshiro
authors.initials: T
authors.lastname: Sakakibara
authors.affiliation: Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Haga
authors.affiliation: Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan.
authors.forename: Etsuji
authors.initials: E
authors.lastname: Yamamoto
authors.affiliation: Graduate School of Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Amitsuka
authors.affiliation: Condensed Matter Theory Laboratory, RIKEN, Wako, Saitama 351-0198, Japan.
authors.forename: Yasumasa
authors.initials: Y
authors.lastname: Tsutsumi
authors.affiliation: Department of Physics, Okayama University, Okayama 700-8530, Japan.
authors.forename: Kazushige
authors.initials: K
authors.lastname: Machida