Intrinsic Pinning in the High Field C-Phase of UPt_3

TL;DR

This study investigates the magnetic response of UPt_3 superconductors under high magnetic fields, revealing intrinsic vortex pinning effects in the C-phase that differ from the A/B-phases, with implications for understanding vortex dynamics.

Contribution

The paper provides the first detailed analysis of vortex pinning behavior in the high-field C-phase of UPt_3 using ac magnetic susceptibility measurements.

Findings

Sharp drop in in-phase susceptibility at T_c in low fields

Large peak in out-of-phase susceptibility at T_c

Effective vortex pinning in the C-phase preventing vortex motion

Abstract

We report on the a.c. magnetic response of superconducting UPt_3 in a d.c. magnetic field. At low fields (H < H^*), the in-phase susceptibility shows a sharp drop at $T_c$ followed by a gradual decrease with decreasing temperature, while the out-of-phase component shows a large peak at T_c followed by an unusual broad peak. As the B-C phase line is crossed (H>H^*), however, both the in-phase and out-of-phase susceptibilities resemble the zero-field Meissner curves. We interpret these results in terms of a vortex pinning force which, while comparatively small in the A/B-phases, becomes large enough to effectively prevent vortex motion in the C-phase.