C. D. Bredl

Heavy-fermion superconductivity atT c =2K in the antiferromagnet UPd2Al3

UPd2Al3 is a new heavy-fermion superconductor with a recordTc of 2 K. In addition, it shows a transition to long-range antiferromagnetic order atTN=14 K. Its Sommerfeld coefficient is reduced from γp=210mJ/K2 mole in the paramagnetic to γ0=150mJ/K2 mole in the antiferromagnetic phase.

Superconductivity and Magnetic Order in a Strongly Interacting Fermi-System: URu2Si2

Measurements are reported on the electrical resistivity, susceptibility, dc-Meissner effect and specific heat of the tetragonal U-compound URu2Si2. AtTN≅17 K, an antiferromagnetic phase transition is observed. This magnetically ordered state appears to coexist with superconductivity, which is found belowTc≅1.5 K. An analysis of the upper critical field data reveals rather, unusual properties of both the normal- and the superconducting state. The effective mass of the quasiparticles at low temperatures is substantially enhanced (m*≅50 m0),though the measured low-temperature specific heat coefficient γ does not exceed 65 mJ/K2mol.

A new heavy-fermion superconductor: UNi2Al3

Measurements of the resistivity, susceptibility and specific heat are reported which clearly show that the hexagonal compound UNi2Al3 is a heavy-fermion magnet belowTN=4.6 K and a heavy-fermion superconductor belowTc=1 K.

Specific heat, resistivity and neutron scattering studies in the Kondo lattice CeNi2Ge2

Abstract Specific heat, resistivity and inelastic neutron scattering experiments are reported, which demonstrate that CeNi 2 Ge 2 exhibits a heavy-fermion groundstate which is neither magnetic nor superconducting. The specific heat coefficient γ( T ) reaches 350 mJ/K 2 mol and exhibits a peak at 0.4 K showing that coherence effects become important at low temperatures. The magnetic relaxation rates as measured via the line width in inelastic neutron scattering experiments are strongly enhanced and deviate from a Korringa law behaviour. The Kondo temperature T K ≈ 30 K was determined from the magnetic relaxation rates and from the specific heat data.

Gapless superconductivity and variation of Tc in the heavy-fermion system CeCu2Si2☆

Abstract Polycrystalline samples of CeCu2Si2 exhibit bulk superconductivity carried by “heavy fermions”. While usually Tc ≊ (0.55 ± 0.15) K, a few samples showed considerably lower transition temperatures (Tc ⩾ 0.11 K), which could, however, be raised to usual values by proper heat treatment. We found that lower Tcs are accompanied by both slightly reduced values of the spin-fluctuation temperature of the Ce3+ ions and the phenomenon of “gapless superconductivity”. In agreement with recent results by Aliev et al. [5], a CeCu2Si2 single crystal did not become superconducting above 20 mK, but showed a 20% deficiency in Cu occupation.

UPd2Al3-a new heavy-fermion superconductor with Tc = 2K

Abstract We report measurements on polycrystalline and, for the first time, single-crystalline samples of UPd2Al3, a new heavy-fermion superconductor (HFS) with a record-Tc of 2K and an antiferromagnetic transition at TN = 14K.

4f-conduction electron hybridization in ternary CeTMAl compounds

Abstract We present an investigation of CeTMAl phase diagrams with TMRu, Pd, Pt and Au. Several new compounds have been characterized by measurements of the electrical resistivity ϱ ( T ), the do susceptibility χ ( T ) and, in some cases, the specific heat C ( T ). We find that in the compounds with TMRu, the hybridization strength between 4f and conduction electrons is strong, leading in most compounds to an intermediate valent (IV) state. By contrast, most of the investigated compounds with TMPd, Pt and Au order magnetically indicating a much weaker hybridization strength. However, some of the Pt and especially Pd compounds are very near to the crossover from the magnetic to the non-magnetic regime as deduced from a Kondo-type maximum in the resistivity and a large electronic specific heat at low temperatures.

Magnetic ordering in the heavy-fermion compounds CePtSi2 and CeNiGe2

Abstract The ground state of three CeTMX 2 compounds with CeNiSi 2 structure type was investigated by electrical-resistivity, magnetic-susceptibility and specific-heat measurements. Whereas CeNiSi 2 is an intermediate-valent system, we observe in CePtSi 2 and CeNiGe 2 magnetic ordering in the presence of heavy fermions. The trends in heavy-fermion formation on going from either the 111 or 122 to the 112 compounds are discussed.

Phase transitions in the heavy Fermi-liquid state: CeCu2Si2, UNi2Al3 and UPd2Al3

Abstract We discuss the superconducting and other phase transitions in CeCu 2 Si 2 and UT 2 Al 3 (T: Ni,Pd). For CeCu 2 Si 2 , a novel lattice instability is found to limit the highest T c attainable by appropriate heat treatment. In the UT 2 Al 3 homologs, antiferromagnetism develops at T N = 4.6K (14K) and possibly coexists with heavy-fermion superconductivity below T c = 1K (2K) for T = Ni(Pd).

Phase Diagram of the Superconducting States of U1-xThxBe13

A phase diagram is proposed for the different superconducting states in U1-xThxBe13. It suggests that the transition in UBe13 at Tc = 0.87 K should be associated with the lower transition in U1-xThxBe13 (0.02 < x < 0.06). The specific heat and upper critical field results on UBe13, indeed appear to indicate a second superconducting transition at 0.55 K like in the Th-doped systems. Our analysis is practically independent of the form of the super-conducting pairing.