UC Irvine

Ultrasound studies are reported on the heavy fermion superconductors UPt3, UBe13 and (U, Th)Be13. In UPt3 we find the ultrasound attenuation to vary as T2 well below the transition temperature. This indicates an anistropic, polar-like superconducting state. In pure UBe13 a pronounced attenuation peak appears at Tc which suggests absorption of phonons by collective excitations of the order parameter. At the lower transition in Th-doped UBe13, we find a λ-shaped attenuation maximum. The shape and magnitude are consistent with magnetic order within the (anisotropic) superconducting state. The ordered moment, coexisting with superconductivity is estimated to be small ((0.02-0.05)microB). The variation of the sound velocity in all these compounds can be explained by (1) the large entropy associated with the heavy fermions; (2) the basic thermodynamic relationships of the superconducting transition; and (3) the magnetic order in (U, Th)Be13. © 1985.