Anomalous Field-Angle Dependence of the Specific Heat of Heavy-Fermion Superconductor UPt3

Abstract

We have investigated the field-angle variation of the specific heat C(H, phi, theta) of the heavy-fermion superconductor UPt3 at low temperatures T down to 50 mK, where phi and theta denote the azimuthal and polar angles of the magnetic field H, respectively. For T = 88 mK, C(H, theta=90) increases proportionally to H^{1/2} up to nearly the upper critical field Hc2, indicating the presence of line nodes. By contrast, C(H, theta=0) deviates upward from the H^{1/2} dependence for (H/Hc2)^{1/2} > 0.5. This behavior can be related to the suppression of Hc2 along the c direction, whose origin has not been resolved yet. Our data show that the unusual Hc2 limit becomes marked only when theta is smaller than 30. In order to explore the possible vertical line nodes in the gap structure, we measured the phi dependence of C in wide T and H ranges. However, we did not observe any in-plane angular oscillation of C within the accuracy of dC/C~0.5%. This result implies that field-induced excitations of the heavy quasiparticles occur isotropically with respect to phi, which is apparently contrary to the recent finding of a twofold thermal-conductivity oscillation.

arXiv comment6 pages, 5 figures, Selected for an Editors' Choice

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• Exotic multi-gap structure in UPt${}_3$ unveiled by the first-priniciples analysis
• Sharp magnetization jump at the first-order superconducting transition in Sr2RuO4
• Surface state tunneling signatures in two-component superconductor UPt${}_3$
• Nodal Superconductivity of UTe${}_2$ Probed by Field-Angle-Resolved Specific Heat on a Crystal with $T_{\mathrm{c}}=2.1$ K
• Paramagnetic limit of spin-triplet superconductors