We report magnetoresistance measurements of the heavy electron compound UBe13 above the superconducting transition temperature Tc and below 4 K for pressures P up to 19 kbar and for magnetic fields H up to 9 T. We observe strong negative magnetoresistance at all pressures and temperatures. The resistivity ρ is quadratic in temperature T from Tc up to a maximum temperature of 1 K at 1 bar increasing to 2 K at 19 kbar. The slope of the T2 term decreases with both H and with P. We find that δ(H)≡-[ρ(H)-ρ(0)]/ρ(0) for a given pressure scales as a function of H/T and exhibits power-law behavior over one decade with an exponent of 1.7. In addition, δ(H) at high pressure shows this same power law over a more limited H/T range.

We have used resistance measurements at pressures to 95 kbar and magnetic fields to 8 T to probe the establishment of Kondo coherence in the heavy-fermion Kondo lattice UBe13. With increasing pressure, the negative magnetoresistance characteristic of noninteracting Kondo impurities evolves into the positive magnetoresistance expected for a coherent Kondo lattice. We show that coherence is established by the suppression of inelastic scattering, over a temperature range which expands as pressure decreases the superconducting transition temperature Tc and increases the Kondo temperature Tk. © 1989 The American Physical Society.

At ambient pressure UCd11 undergoes a phase transition near 5 K that is believed to arise from antiferromagnetic order within a strongly correlated electron system. Under moderate hydrostatic pressures, two new phase transitions appear below 5 K that are manifested by anomalies in the temperature-dependent electrical resistivity. We present the evolution of these transitions with pressure, temperature, and magnetic field and discuss possible interpretations of their origin given the pressure dependence of the resistivity and magnetic susceptibility. © 1989 The American Physical Society.

We have measured the temperature dependence of the electrical resistivity of UBe13 for magnetic fields up to 8 T and pressures to 95 kbar. Pressure increases the temperature range over which ρ{variant} = ρ{variant}0 + AT2, while the pressure and magnetic field dependences of ρ{variant}0 and A reflect changes in the quasiparticle interactions. © 1990.

We report results of neutron powder diffraction experiments on the heavy-electron magnet UCd11 at temperatures above and below its ordering temperature. These measurements set an upper limit on the ordered moment of 1.5μB/U. © 1988.

Electrical resistivity ρ measurements under pressure have been carried out on the high-temperature superconductor YBa2Cu3O7 - δ as a function of temperature T between 1 and 300 K at various pressures between 8 kbar and 149 kbar. The superconducting transition temperature Tc increases almost linearly with pressure at the rate dTc/dP ∼- 0.13 K/kbar. The onset of Tc, defined as the temperature at which ρ(T) drops to 90% of its extrapolated normal state value, increases from ∼95 K at 8 kbar to 107 K at 149 kbar. These results suggest that higher pressures will yield yet higher values of Tc. © 1988 Springer-Verlag.

We have investigated the source of the anisotropic susceptibility of UZn8.5 by preparing single crystals of UxTh 1-xZn8.5 for small x. Preliminary indications are that anisotropic exchange, rather than crystal field effects, are responsible for the anisotropy, but possible impurity contributions to the (anisotropic) susceptibility of the ThZn8.5 do not permit a stronger statement. Further measurements for small x show that both the electronic specific heat and the susceptibility at low temperature are strongly enhanced, and that Kondo-type resistivity minima are observed. The enhancements are somewhat reduced in the concentrated system UZn8.5.

The electrical resistivity of the heavy-electron superconductor UBe13 was investigated over temperatures ranging from 1 to 300 K and at high pressures from 12 to 152 kbar. The temperature, Tmax, at which attains a maximum increases linearly with pressure at two limiting rates: 0.25 K/kbar below 30 kbar and 0.65 K/kbar above 30 kbar. At low temperatures, the -versus-T data can be described by the expression =0+AT2 over a temperature interval of 1 K at 12 kbar to more than 16 K at 152 kbar. The coefficient A can be related to the Fermi-liquid energy scale T* by A-1/2 T*. The pressure dependence of A-1/2 also increases linearly with pressure at two limiting rates, with a crossover at about 50 kbar. The similarity in the pressure dependences of Tmax and A-1/2 suggests that both parameters are proportional to a single energy scale, while the changes in pressure dependence of Tmax and A-1/2 may represent a crossover from heavy-fermion to intermediate-valence behavior. © 1990 The American Physical Society.

The electrical resistivity of the heavy-electron superconductor UBe13 has been measured at temperatures T between 0.1 and 300 K for pressures P to 16 kbar and in magnetic fields H up to 9 T. The temperature Tmax at which shows a maximum increases linearly with P at H=0 and with H2 for P=14.8 kbar. The resistivity, when normalized to its value at Tmax(P), scales as a function of reduced temperature T/Tmax(P) from 1 K to 1/41.4Tmax. At P=14.8 kbar, the magnetoresistance -[R(H)-R(0)]/R(0) behaves as a universal function of H/T for 1T6 K and 0