No abstract

The thermal conductivity of the heavy-fermion superconductor CeCoIn5 has been studied in a magnetic field rotating within the 2D planes. A clear fourfold symmetry of the thermal conductivity which is characteristic of a superconducting gap with nodes along the ( +/- pi,+/- pi) directions is resolved. The thermal conductivity measurement also reveals a first-order transition at H(c2), indicating a Pauli limited superconducting state. These results indicate that the symmetry most likely belongs to d(x(2)-y(2)), implying that the anisotropic antiferromagnetic fluctuation is relevant to the superconductivity.

We observed de Haas-van Alphen (dHvA) oscillation in both the normal and superconducting mixed states of a heavy-fermion superconductor CeCoIn5. The Fermi surfaces are found to consist of nearly cylindrical Fermi surfaces and small ellipsoidal ones, reflecting the unique tetragonal crystal structure. The detected cyclotron masses of 5-87 m0 for these Fermi surfaces are extremely large, and correspond to a large electronic specific heat coefficient of about 1000 mJ K-2 mol-1. The cyclotron masses are also found to be field dependent in both the normal and mixed states.

No abstract

Using the de Haas-van Alphen effect we have measured the evolution of the Fermi surface of BaFe2(As1-xPx){2} as a function of isoelectric substitution (As/P) for 0.41

No abstract

dc magnetization measurements on CeCoIn 5 reveal a first-order phase transition at H c2 for both Hʈa and c axes in the isothermal magnetization M (H) below 0.7 K, indicating a strong Pauli paramagnetic suppression in the even-parity pairing. M (T) in the normal state above H c2 exhibits non-Fermi-liquid behavior down to 150 mK, implying the existence of antiferromagnetic fluctuations behind the unconventional superconductivity. We observed an unusual peak effect for Hʈc in fields 5-30 kOe below 150 mK(ϭ0.06T c ), whose anomalous temperature dependence cannot be simply explained by ordinary mechanisms.Since in 1979, 1 HF superconductivity has been attracting interest in the field of strongly correlated electron systems. Recent experimental and theoretical progress indicates that most of the HF superconductors are likely to be of an unconventional type. Until recently, to our best knowledge, CeCu 2 Si 2 was the only Ce-based HF superconductor at ambient pressure. The superconductivity in CeCu 2 Si 2 , however, is rather difficult to understand because of the complicated magnetic phase diagram. 2 Quite recently, two tetragonal Ce-based HF compounds have been discovered by Petrovic et al. to become superconducting at ambient pressure: CeXIn 5 ͓XϭIr ͑Ref. 3͒ and Co ͑Ref. 4͔͒. To our best knowledge, CeCoIn 5 has the highest T c (ϭ2.3 K) among the HF superconductors known at present. The specific heat, 4 thermal conductivity, 6 and NMR relaxation rate 8 of CeCoIn 5 show power-law temperature dependencies below T c , suggesting an unconventional superconductivity with anisotropic energy gap. Very recently, the NMR Knight-shift measurement 7,8 has revealed even-parity pairing in the superconducting state, and the angle-dependent thermal-conductivity measurement 9 has identified that the gap symmetry is k x 2 Ϫk y 2 , pointing to the fact that the pairing interaction is mediated by magnetic fluctuations. An interesting observation with respect to this point is the non-Fermiliquid ͑NFL͒ behavior in the specific heat divided by temperature C/T, showing a remarkable upturn on cooling when the superconductivity is suppressed by magnetic field. 4,5 To our best knowledge the origin of the NFL behavior has not been clarified yet.One of the features of the HF superconductors is that the orbital limiting field is relatively high despite low T c , because of the small Fermi velocity of the carriers. In addition, the HF superconductors possess quite large normal-state paramagnetic susceptibility at sufficiently low temperature, reflecting the high density of states. These facts lead to an interesting situation in which the paramagnetic energy near H c2 becomes a significant fraction of the superconducting condensation energy. 10,11 It was theoretically pointed out that a second-order transition at H c2 changes into a first-order one below ϳ0.56 T c for the singlet pairing, provided that the normal-state spin susceptibility is large enough. 12,13 Subsequent theoretical studies predicted that in the case of a clean limit (lӷ 0 ) a firs...

To clarify the superconducting gap structure of the spin-triplet superconductor Sr2RuO4, the in-plane thermal conductivity has been measured as a function of relative orientations of the thermal flow, the crystal axes, and a magnetic field rotating within the 2D RuO2 planes. The in-plane variation of the thermal conductivity is incompatible with any model with line nodes vertical to the 2D planes and indicates the existence of horizontal nodes. These results place strong constraints on models that attempt to explain the mechanism of the triplet superconductivity.