R. N. Kleiman

Magnetic fluctuations and the superconducting transition in the heavy-fermion material UPd2Al3

Abstract Inelastic neutron scattering has been performed on single crystals of the heavy-fermion superconductor UPd 2 Al 3 . The antiferromagnetically ordered state is characterized by an acoustic spin wave mode with no gap. The low-frequency magnitude excitations are unaffected by the transition to a superconducting state despite coupling to the conduction electrons as evidenced by the significant damping.

Low‐temperature specific heat and thermal expansion in the frustrated garnet Gd3Ga5O12

Gd3Ga5O12 is strongly frustrated, possessing a Curie–Weiss temperature of −2.3 K, while not ordering down to 25 mK, in zero field. Specific‐heat and thermal‐expansion measurements were made as a function of temperature (0–2 K) and magnetic field (0–2 T). The unusual phase diagram of this material, reported in the susceptibility measurements of Hov, Bratsberg, and Skjeltorp [J. Magn. Magn. Mater. 15–18, 455 (1980)], is verified by the present thermal behavior.

Neutron diffraction from the vortex lattice in the heavy fermion superconductor UPt3 (invited) (abstract)

The heavy fermion superconductor UPt3 is thought to have a d‐wave pairing ground state. The principal experimental evidence for this consists of the anisotropy of the power‐law behavior observed in transverse ultrasound and μ+ SR measurements. The observation of a complex phase diagram in the superconducting state in ultrasound, torsional oscillator, and specific heat measurements may be a further indication of an unconventional pairing state. Theoretical investigations suggest the possibility of vortex lattices that are unconventional in their symmetry, their quantization, or the structure of their composite vortex cores. Transitions between such exotic vortex lattices are in principle allowed and could explain the observed features at H≊0.6 Hc2 (for H∥c) and H≊0.3Hc2 (for H⊥c). Neutron diffraction is an ideal bulk probe of the microscopic properties of the vortex lattice. We have studied the vortex lattice with H⊥c and T≊50 mK in the field range 0.75

Small angle neutron scattering from the vortex lattice in 2H‐NbSe2 (invited) (abstract)

We report on small angle neutron scattering studies of the flux‐line lattice in single crystal 2H‐NbSe2. For fields inclined with respect to the c axis, we find distortions and form factors consistent with Ginzburg–Landau corrections to the London equations with a mass anisotropy Γ=10.1±0.9. The flux lattice orientation, however, remains pinned to the crystal lattice for all tilts studied, in disagreement with the orientation defined by anisotropic London theory. For fields below 2 kG parallel to the c axis, the peaks are no longer resolution limited. The correlation lengths extracted are history dependent, and show that the lattice is annealed when a current greater than the critical current is applied. This occurs both when a direct transport current is used, or an induced current in a zero field cooled experiment. The annealing is seen in both the transverse and longitudinal correlation lengths, and calls into question the relationship between the Larkin–Ovchinnikov correlation length and the measured ...

Superconductivity of UPt3 studied by μ+SR and neutron scattering (abstract)

The magnetic field penetration depth λ in single‐crystalline UPt3 has been measured by muon spin relaxation ( μ+SR). The temperature dependence of λ−2 is nonexponential and anisotropic decreasing from its T=0 value proportional to T when measured perpendicular to the c axis but with a higher‐power ∥c. Our data can be accounted for in detail by a superconducting gap with a line of nodes in the basal plane and axial point nodes. By neutron scattering we furthermore show that the antiferromagnetic order parameter of UPt3 is perturbed by the development of superconductivity. We discuss the implications of these results on the symmetry of the superconducting states of UPt3.