Symmetry of Order Parameters in Multiband Superconductors LaRu4As12 and PrOs4Sb12 Probed by Local Magnetization Measurements

Abstract

The temperature dependencies of the lower critical field Hc1(T) of several filled-skutterudite superconductors were investigated by local magnetization measurements. While LaOs4As12 and PrRu4As12 exhibit the Hc1(T) dependencies consistent with the single-band BCS prediction, for LaRu4As12 (the superconducting temperature Tc=10.4 K) with a similar three-dimensional Fermi surface, we observe a sudden increase in Hc1(T) deep in a superconducting state below about 0.32Tc. Remarkably, a rapid rise of Hc1(T) at approximately the same reduced temperature 0.27Tc is also found for the heavy-fermion compound PrOs4Sb12 (Tc≃1.78 K), in fair accord with the earlier macroscopic study. We attribute the unusual Hc1(T) dependencies of LaRu4As12 and PrOs4Sb12 to a kink structure in their superfluid densities due to different contributions from two nearly decoupled bands. Whereas LaRu4As12 is established as a two-band isotropic s-wave superconductor, nonsaturating behavior of Hc1(T) is observed for PrOs4Sb12, indicative of an anisotropic structure of a smaller gap. For this superconductor with broken time-reversal symmetry, our findings suggest a superconducting state with multiple symmetries of the order parameters.

Source-reported materials — not catalogue approval

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