AC susceptibility and anisotropic flux pinning in uncoventional superconductor UPt3

Abstract

AC susceptibility measurements have been carried-out on single-crystalline samples of UPt 3 doped with 11% boron. The low-amplitude susceptibility is nearly independent on the ac field amplitude and, hence, it is related to the low-frequency complex conductivity. At large ac field, strong nonlinearities characterize the electrodynamie response. The critical state model is, however, not sufficient for analysis of the results. A reactive component of the conductivity must be included for a consistent description of the susceptibility. The strong anisotropy of the ac response observed at low fields is also present for fields near the upper critical field, FL2.

Intrinsic pinning in the high-fieldCphase ofUPt3

“…At low excitations, the aforementioned features in χ ′ and χ ′′ as a function of H dc are absent; the in-phase susceptibility drops at T c to the strong pinning value both above and below the tetracritical point and the out-of-phase component exhibits low dissipation in all three phases. Somewhat similar effects have previously been noted [6] in UP t 3 . These data emphasize the fact that the phenomena presented here are non-linear in the sense that they are observed only when vortices are strongly perturbed about there pinning sites.…”