The lower and upper critical fields in the heavy electron superconductor UPt 3

Abstract

We have measured both the lower and upper critical fields in single crystals of UPt 3 within a single technique for field orientations both parallel and perpendicular to the c-axis. The ‘kink’ or the upward curvature in the upper critical field, H c 2 for H‖basal plane seen in earlier measurements is found to be sharper in single crystals of better quality. Correlated with this feature in H c 2 we also find a ‘kink’ in the lower critical field, H c 1 for H‖basal plane. These observations add further support to the two-dimensional order-parameter model for UPt 3 proposed to explain the recent observation of two jumps in the specific heat. For the orthogonal field orientation H‖ c-axis we find no such anomaly in H c 1 within the resolution of our measurements.