[en] Heavy fermion superconductors are largely studied for their unconventional ground states. We present results on the skutterudite compound PrOs₄Sb₁₂ (T_c ∼ 1.8K), and on the heavy-fermion CeCoIn₅ (T_c ∼ 2.3K), where both the low field and the low temperature behaviour of their thermal conductivity yield evidence for multigap superconductivity.

[en] In the icosahedral phases i-AlCuFe, i-AlPdMn and i-AlPdRe, the electrical conductivity is in the same range as for doped semiconductors. Strong similarities are observed between the direct and tunneling conductivity for the i-AlPdRe phase and for disordered systems on both sides of the metal–insulator (MI) transition.

[en] We report on tunneling spectroscopy measurements using a scanning tunneling microscope (STM) on the spin triplet superconductor Sr₂RuO₄. A fully open gap, close to the Bardeen-Cooper-Schrieffer (BCS) value, is found, which disappears at the bulk T_c=1.5 K. The results are discussed in the framework of recent multigap scenarios for an unconventional spin triplet superconductor.

[en] The pressure-temperature phase diagrams of the heavy fermion antiferromagnet CeRhIn₅ and the heavy fermion superconductor CeCoIn₅ have been studied under hydrostatic pressure by ac calorimetry and ac susceptibility measurements using diamond anvil cells with argon as the pressure medium. In CeRhIn₅, the use of a highly hydrostatic pressure transmitting medium allows for a clean simultaneous determination by a bulk probe of the antiferromagnetic and superconducting transitions. We compare our new phase diagram with the previous ones, discuss the nature (first or second order) of the various lines, and the coexistence of antiferromagnetic order and superconductivity. The link between the collapse of the superconducting heat anomaly and the broadening of the antiferromagnetic transition points to an inhomogeneous appearance of superconductivity below P_c ∼ 1.95 GPa. Homogeneous bulk superconductivity is only observed above this critical pressure. We present a detailed analysis of the influence of pressure inhomogeneities on the specific heat anomalies which emphasizes that the observed broadening of the transitions near P_c is connected with the first-order transition. For CeCoIn₅ we show that the large specific heat anomaly observed at T_c at ambient pressure is suppressed linearly at least up to 3 GPa

[en] We have performed transport and susceptibility measurements on single-crystal CeNi₂ Ge₂ under high pressure and magnetic field. Under pressure a 30% decrease of the resistivity is found below 300 mK which could be due to the onset of superconductivity. Assuming this we have established the phase diagram of the superconducting phase under pressure and magnetic field. The analysis of H_c2 and the slope at T_c in comparison to a previously published report of superconductivity at ambient pressure might indicate a change in the order parameter with pressure. The normal state resistivity at ambient pressure does not show a quadratic temperature dependence. Under pressure a quadratic dependence is found and we show that the parameters of the resistivity and the susceptibility obey a simple scaling law. This scaling breaks down however when approaching the magnetic instability. (author)

[en] We report the upper critical field, H_c2, of the non-centrosymmetric compound CeCoGe₃ by resistivity measurements under high pressure of 7.1 GPa, for H along c and a axis, and for a magnetic field up to 17 T. H_c2 is very anisotropic, saturating at low temperature for H along the a axis and linear for H along the c axis. Very high H_c2(T) is observed for H along the c axis, with a huge value of the slope dH_c2/dT = -47 ± 1.3 T/K, the highest ever reported if normalized to the superconducting temperature of 0.65 K. This is most probably related to a conjunction of a heavy fermionic state and the absence of the Pauli limitation. A fit of H_c2(T) shows that the curves for a and c axis can be reproduced with a moderate coupling Eliashberg theory.

[en] We present evidence which casts doubt on the intrinsic nature of the double superconducting transition (T_c1=1.89K and T_c2=1.72K) of the filled skutterudite compound PrOs₄Sb₁₂. Because of similar behaviors of T_c1 and T_c2, the magnetic field and pressure dependence of the transitions are not conclusive. Further characterizations show a wide range of values of the ratio of the two specific heat jumps ΔC(T_c1)/ΔC(T_c2) on crystals from different batches and even within the same batch. Moreover, one sample exhibits a single sharp transition of 18mK in width at T_c=1.73K. It has been characterized by specific heat, AC susceptibility and resistivity. A normalized specific heat jump ΔC(T_c)/C(T_c) of 25% which matches the sum of the two specific heat jumps in the other samples has been obtained