Ultrasonic Attenuation in UPt3

Abstract

We report measurements of the ultrasonic absorption in UP${\mathrm{t}}_3$ through the superconducting transition. The attenuation varies as $T^2$ at low temperature and is inconsistent with the identification of UP${\mathrm{t}}_3$ as a singlet superconductor. Our results can be well explained by assuming that UP${\mathrm{t}}_3$ is an anisotropic (triplet) superconductor in a polarlike state, where the gap vanishes along a line on the Fermi surface.