After recognizing the occurrence of heavy electrons in metals at low temperatures it was found that they may undergotransitions to a superconducting state. Details of one of these materials, UBe13 are shown and discussed. A comparison of experimental data of the specific heat and theoretical calculations suggests that the superconducting state is the electronic analogue of the A phase of superfluid 3He. The influence of impurities on the superconducting state of UBe13 and properties of similar compounds which are not superconductors but order magnetically instead support these ideas. © 1984 Elsevier Science Publishers B.V.

The strong influence of changes of the chemical composition on the formation of a heavy-electron ground state is demonstrated in uranium intermetallic compounds crystallizing in the cubic AuBe5 structure. The most spectacular effect is the large enhancement of the low-temperature electronic specific heat in UPt5 when one Pt atom per formula unit is replaced by Au. UAuPt4 may be a heavy-electron superconductor. © 1987 The American Physical Society.

Electrical-resistivity, magnetic-susceptibility, and specific-heat data reveal that UBe13 is superconducting below 0.85 K. Highly anomalous low-temperature electronic properties in both the normal and superconducting states result in an enormous electronic specific-heat coefficient γ=1.1 J/mole K2 and a corresponding magnetic susceptibility χ=1.5×10-2 emu/mole. The superconducting state appears to be extremely stable with an initial slope of the temperature derivative of the critical field (Hc2T)Tc=-257 kOe/K. © 1983 The American Physical Society.

Measurements of the magnetic susceptibility, specific heat, and electrical resistivity of U2Zn17 reveal a magnetic phase transition of this compound at 9.70 K. Details of the specific heat indicate that the ordering occurs among electrons whose energy spectrum shows an anomalously large density of states at the Fermi energy. This result is of interest with regard to the occurrence of superconductivity in similar systems. © 1984 The American Physical Society.

We report results of specific-heat measurements and the observation of a new phase transition in the superconducting state of U1-xThxBe13 compounds for a narrow range of x values. Although the nature of this transition cannot be unambiguously established, its occurrence is important with regard to the characterization of the superconducting state in these compounds. © 1985 The American Physical Society.

Recent work intended to investigate a Fermi-liquid-type low-temperature state in uranium intermetallic compounds is reviewed. In form of a comparison of physical properties with those of CeAl3, the prototype heavy-electron system, some details concerning the occurrence of this heavy-electron state are discussed. Special attention is then given to experimental data giving evidence for superconductivity or magnetic order, both involving these heavy electrons. The possibility of unconventional superconductivity in these systems is supported by increasing experimental evidence.

The formation of a heavy-electron state in a magnetically ordered material is established by measurements of the low-temperature specific heat of UCu5 and UAgCu4. In UCu5 this state undergoes a continuous but hysteretic phase transition which removes parts of the Fermi surface with a high density of electronic states and leads to a resistivity increase of almost an order of magnitude. © 1985 The American Physical Society.

Small amounts of Th and Lu impurities considerably affect both the low-temperature normal and the superconducting states of UBe13. Th enhances the electronic specific-heat parameter for T0 K and leads to a second phase transition in the superconducting state. Lu substitution for U suppresses superconductivity quite effectively, and also is sizably reduced. Bulk measurements confirm the unusual Hc2(T) curve of UBe13 that was previously obtained from electrical resistivity experiments. © 1986 The American Physical Society.

Results of measurements of the electrical resistivity ρ{variant} between 0.04 and 1 K and the specific heat cp between 0.06 and 1 K of annealed polycrystalline CeCu6 are reported. ρ{variant} varies proportional to T2 below 0.1 K but is linear in T above 0.6 K. The specific heat is proportional to T below 0.5 K and the electronic specific-heat parameter γ = 1.53 J mole K2. © 1985.

The high-temperature structural phase transition in URe2 is only moderately influenced by thorium impurities at low concentrations but disappears rapidly when the thorium content exceeds 25%. Replacing thorium in ThRe2 by uranium reduces its critical temperature for the onset of superconductivity but much less drastically than do uranium impurities in metallic thorium. A comparison of the low-temperature specific heats of URe2 and ThRe2 indicates that the density of f-electron states at the Fermi energy EF in URe2 is not large and that the f electrons in URe2 behave similarly to d electrons in non-magnetic d transition metals. © 1986.