We report on low-temperature thermal conductivity of the noncentrosymmetric superconductor LaRhSi3 (TC = 2.3K), which is a paramagnetic analog of the pressure-induced superconductor CeRhSi3. In the normal state (either in zero field above Tc, or in magnetic field above Hc2), the thermal conductivity k is mostly due to electrons, and shows a nearly T-linear dependence. In the superconducting state, k decreases exponentially below Tc, and crosses over to κ T2 behavior at T ≪ Tc. The temperature dependence of thermal conductivity of LaRhSi3 is similar to that of a number of conventional s-wave superconductors. The field dependence of the residual linear term κ0/T as a function of magnetic field suggests that LaRhSi3 has no nodes in the superconducting gap. © Published under licence by IOP Publishing Ltd.

A long-standing theoretical prediction is that in clean, nodal unconventional superconductors the magnetic penetration depth λ, at zero temperature, varies linearly with magnetic field. This non-linear Meissner effect is an equally important manifestation of the nodal state as the well studied linear-in-T dependence of λ, but has never been convincingly experimentally observed. Here we present measurements of the nodal superconductors CeCoIn₅ and LaFePO which clearly show this non-linear Meissner effect. We further show how the effect of a small dc magnetic field on λ(T) can be used to distinguish gap nodes from non-nodal deep gap minima. Our measurements of KFe₂As₂ suggest that this material has such a non-nodal state.