We have measured the magnetostriction, L(H), of a single crystal of the Heavy Fermion superconductor, UBe13, using an all silicon high precision capacitance dilatometer. We find clear evidence for a transition to an antiferromagnetic state at TN ∼ 8.8K, which is suppressed in a field by dTN/dH ∼ 0.36K/T. At low temperatures we observe pronounced magnetostrictive oscillations, which we believe are de Haas-van Alphen oscillations due to an unusual aspect of the Fermi surface. © 1990.

We have measured the magnetostriction L(H) of a single crystal of the heavy-fermion superconductor UBe13 using an all-silicon high-precision capacitance dilatometer. We find clear evidence for a transition to an antiferromagnetic state at TN 8.8 K, which is suppressed in a field by dTN/dH 0.36 K/T. At low temperatures we observe pronounced magnetostrictive oscillations, which we believe are de Haasvan Alphen oscillations due to an unusual aspect of the Fermi surface. © 1990 The American Physical Society.

Sound propagation in the heavy-fermion superconductor UBe13 is studied at frequencies from 0.9 to 2.4 GHz and temperatures from 0.01 to 100 K. A peak in the acoustic attenuation is observed below the superconducting transition of 0.9 K, instead of the rapid drop expected for a BCS superconductor. Absorption into a collective mode of a nonsinglet, anisotropic superconductor is proposed. © 1985 The American Physical Society.

Experimental studies are discussed which shed light on the nature of the heavy fermion normal state, the occurrence of heavy fermion superconductivity and anomalous properties of the superconducting state: i) Magnetization and magnetoresistance of the Kondo lattice UBe13 demonstrate the breakdown of a description in terms of a single energy scale TK. Here TK becomes temperature dependent below ≃ 10 K, and the canonical relationship between R(H) and M(H) does not hold. ii) Superconductivity in UPt3 occurs at the borderline to magnetism: spin-density wave-like instabilities are induced by a few percent of Th or Au, whereas mass enhancement and susceptibility are rapidly reduced by Ir substitution. This suggests that spin fluctuations, rather than phonons, are important in mediating superconducting pairing of heavy fermions in UPt3. iii) The possibilities of noncubic strain induced by anisotropic superconductivity in UBe13 is investigated by ultrasound experiments. The suggestion of tetragonal strain in (U, Th)Be13 is found to be not applicable, and observed frequency and amplitude dependent absorption anomalies at T ≪ Tc might reflect domain wall motion. © 1987.

The authors report measurements of the ultrasonic attenuation and sound velocity through the superconducting transition of UPt//3. The attenuation varies as T**2 at low temperatures and is inconsistent with the identification of UPt//3 as a singlet superconductor. Below T//c the sound velocity varies roughly as T**3 and above T//c as T**2. The results indicate that UPt//3 is an anisotropic (triplet) superconductor in a polar-like state.

We report measurements of the ultrasonic absorption in UPt3 through the superconducting transition. The attenuation varies as T2 at low temperature and is inconsistent with the identification of UPt3 as a singlet superconductor. Our results can be well explained by assuming that UPt3 is an anisotropic (triplet) superconductor in a polarlike state, where the gap vanishes along a line on the Fermi surface. © 1984 The American Physical Society.

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.

Ultrasound experiments were performed on single crystals of the heavy Fermion superconductor UPt3. From the ultrasound attenuation below Tc, a quasiparticle density of states linear in energy is deduced, which we interpret as due to an anisotropic polar-like (triplet) superconducting state. This is further supported by the agreement of the only fitting parameter Δ0/kTc with the theoretical value for polar p-wave pairing. The attenuation in the normal state gives the electron-phonon interaction strength and the product of the deformation potential times the effective mass is found to be the same as for ordinary ''light'' Fermion systems. The observed variations of the sound velocity are discussed.

Quantitative studies of ultrasound absorption in the heavy-fermion state of UPt3 and UBe13 are reported. The magnitude of the absorption due to electrons in the normal state is not enhanced compared to that of ordinary metals, indicating a cancellation of the mass enhancement by a reduction of the electron-phonon coupling parameter. This implies that the mass enhancement is described by a different Landau Fermi-liquid parameter than in He3. The T2 variation of the normal-state sound velocity at lowest temperatures is consistent with the large electronic specific heat. © 1986 The American Physical Society.