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.

We report microwave surface impedances of FeSe0.4Te0.6 single crystals measured at 12, 19, and 44 GHz. The penetration depth exhibits a power law behavior, δλL = λL(T )−λL(0) ∝ CT n with an exponent n ≃ 2, which is considered to result from impurity scattering. This behavior is consistent with s±-wave pairing symmetry. The temperature dependence of the superfluid density largely deviates from the behavior expected in the BCS theory. We believe that this deviation is caused by the crossover from the dirty regime near Tc to the clean regime at low temperatures, which is supported by the rapid increase of the quasiparticle scattering time obtained from the microwave conductivity. We also believe that the previously published data of the superfluid density can be interpreted in this scenario.

We report results of microwave surface impedance measurements of LiFeAs single crystals. The in-plane penetration depth depends on temperature exponentially at low temperatures, which strongly suggests that this material has the nodeless superconducting gap. The temperature dependence of the superfluid density indicates that LiFeAs is a multi-gap superconductor with at least two isotropic gaps. In addtion, the real part of the microwave conductivity exhibits a large enhancement below $T_\mathrm{c}$, indicating that the quasi-particle relaxation time, $\tau$, increases rapidly below $T_\mathrm{c}$. We believe that this enhancement is rather common to all superconductors where an inelastic scattering is dominant above $T_\mathrm{c}$, irrespective of the strength of the electron correlation.Comment: 13 pages, 3 figure

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