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

作者：Kittaka Shunichiro^*; An Koji; Sakakibara Toshiro; Haga Yoshinori; Yamamoto Etsuji; Kimura Noriaki; Onuki Yoshichika; Machida Kazushige

来源：Journal of the Physical Society of Japan, 2013, 82(2): 024707.

DOI：10.7566/JPSJ.82.024707

• UPt3
• spin-triplet superconductivity
• superconducting gap
• upper critical field
• specific heat

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 degrees) increases proportionally to root H up to nearly the upper critical field H-c2, indicating the presence of line nodes. By contrast, C(H, theta = 0 degrees) deviates upward from the root H dependence for root H/H-c2 greater than or similar to 0.5 . This behavior can be related to the suppression of H-c2 along the c direction, whose origin has not been resolved yet. Our data show that the unusual H-c2 limit becomes marked only when theta is smaller than 30 degrees. 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 Delta C/C similar to 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 kappa(phi) oscillation.

• 出版日期2013-2