ULTRASOUND STUDIES OF THE HEAVY FERMION SUPERCONDUCTORS UPT3, UBE13 AND (U,TH)BE13

Abstract Ultrasound studies are reported on the heavy fermion superconductors UPt 3 , UBe 13 and (U, Th)Be 13 . In UPt 3 we find the ultrasound attenuation to vary as T 2 well below the transition temperature. This indicates an anistropic, polar-like superconducting state. In pure UBe 13 a pronounced attenuation peak appears at T c which suggests absorption of phonons by collective excitations of the order parameter. At the lower transition in Th-doped UBe 13 , 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)micro B ). 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)Be 13 .