Constraints on the Strain-Dependence of the UPt ₃ Superconducting Transition From Longitudinal-Ultrasound Measurements

Abstract

We present measurements of longitudinal ultrasound in UPt3 along both the a- and c-axis in the region of the two superconducting transitions, Tc+ and Tc*. Using expressions from a model for the double superconducting transition, our measurements constrain the strain-dependences of a number of parameters. In particular, these constraints imply that the observed anisotropy in the stress-dependence of Tc* results from anisotropy in the elastic compliance tensor, rather than anisotropy of the superconducting order parameter. We also report an anomalous lattice softening below 100 mK.