title: Omnidirectional Measurements of Angle-Resolved Heat Capacity for Complete Detection of Superconducting Gap Structure in the Heavy-Fermion Antiferromagnet UPd_{2}Al_{3}.
abstract: Quasiparticle excitations in UPd_{2}Al_{3} were studied by means of heat-capacity (C) measurements under rotating magnetic fields using a high-quality single crystal. The field dependence shows C(H)∝H^{1/2}-like behavior at low temperatures for both two hexagonal crystal axes, i.e., H∥[0001] (c axis) and H∥[112[over ¯]0] (a axis), suggesting the presence of nodal quasiparticle excitations from heavy bands. At low temperatures, the polar-angle (θ) dependence of C exhibits a maximum along H∥[0001] with a twofold symmetric oscillation below 0.5 T, and an unusual shoulder or hump anomaly has been found around 30°-60° from the c axis in C(θ) at intermediate fields (1≲μ_{0}H≲2  T). These behaviors in UPd_{2}Al_{3} purely come from the superconducting nodal quasiparticle excitations, and can be successfully reproduced by theoretical calculations assuming the gap symmetry with a horizontal linear line node. We demonstrate the whole angle-resolved heat-capacity measurements done here as a novel spectroscopic method for nodal gap determination, which can be applied to other exotic superconductors.
authors.affiliation: Institute for Solid State Physics (ISSP), The 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), The 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), The University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Toshiro
authors.initials: T
authors.lastname: Sakakibara
authors.affiliation: Department of Basic Science, The University of Tokyo, Meguro, Tokyo 153-8902, Japan.
authors.forename: Yasumasa
authors.initials: Y
authors.lastname: Tsutsumi
authors.affiliation: Departement of Physics, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Nomoto
authors.affiliation: Department of Physics, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Ikeda
authors.affiliation: Department of Physics, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan.
authors.forename: Kazushige
authors.initials: K
authors.lastname: Machida
authors.affiliation: Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313, Japan.
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Homma
authors.affiliation: Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313, Japan.
authors.forename: Dai
authors.initials: D
authors.lastname: Aoki