S.-W. Lin H. Zhang M. Levy Bimal K. Sarma
Phys. Dept., Univ. of Wisconsin, P.O. Box 413, Milwaukee, WI 53201
C. Jin D. M. Lee
Cornell Univ., Ithaca, NY 14853
Ultrasonic measurements have been used very successfully in investigating multi-phase superconductivity in the heavy fermion compound UPt[sub 3]. Further probing of the superconducting properties in UPt[sub 3] demands even higher resolution in both ultrasonic velocity and attenuation measurements. In order to achieve this, a new approach was used in measuring ultrasonic velocity and attenuation, in which a digital dynamic control technique was utilized in the conventional pulse-echo method. With this approach, longitudinal ultrasonic velocity and attenuation of frequencies up to 450 MHz were measured on a single crystal UPt[sub 3] sample in the superconducting state. The overall resolution in the velocity measurement is in the order of 0.1 ppm. This enables us to determine a complex superconducting phase diagram for UPt[sub 3] with unprecedented accuracy. Superconducting phase boundary lines were traced even within the transition width. The critical property of converging phase transition lines is thus determined unambiguously. This in turn provides crucial information for the understanding of unconventional superconductivity in UPt[sub 3]. [Work at UWM supported by ONR and at Cornell by NSF.]