ASA 124th Meeting New Orleans 1992 October

3pPA1. Ultrasonic measurements in superconducting UPt[sub 3].

S. Adenwalla

Dept. of Phys. and Astron., Northwestern Univ., Evanston, IL 60208

S.-W. Lin

Univ. of Wisconsin---Milwaukee, Milwaukee, WI 53201

Z. Zhao

J. B. Ketterson

Northwestern Univ., Evanston, IL 60208

M. Levy

Bimal K. Sarma

Univ. of Wisconsin---Milwaukee, Milwaukee, WI 53201

Ultrasonic measurements on the heavy fermion superconductors have proved a useful tool in elucidating the nature of the superconducting state. Earlier measurements of sound attenuation in superconducting UPt[sub 3] showed power-law temperature dependences (rather than an exponential temperature dependence as expected for a BCS type superconductor), indicating the presence of nodes in the gap. Subsequent ultrasonic measurements have shown indications of phase transitions within the superconducting state. In particular, these ultrasonic velocity measurements show the presence of three superconducting phases in the mixed state. The size of the velocity jump can be related to the heat capacity jump. Further, using a thermodynamic analysis it is possible to deduce the order of the phase transition lines. [Work at NU supported by NSF, and the work at UWM supported by ONR.]