Observation of a low-temperature resonance peak in ultrasonic attenuation ofUPt3

Abstract
We report measurements of the temperature dependence of the ultrasonic attenuation in normal-state UPt3. At about 12 K a pronounced longitudinal absorption peak is observed. Such a peak does not appear for transverse-acoustic waves. Our experimental results can be well explained by a narrow resonance in the quasiparticle excitation spectrum near the Fermi energy and are consistent with the enhanced specific-heat coefficient.