Multigap superconductivity in ThAsFeN investigated using μSR measurements

We have investigated the superconducting ground state of the newly discovered superconductor ThFeAsN with a tetragonal layered crystal structure using resistivity, magnetization, heat capacity, and transverse-field muon-spin rotation (TF-mu SR) measurements. Our magnetization and heat-capacity measurements reveal an onset of bulk superconductivity with T-c similar to 30 K. A nonlinear magnetic-field dependence of the specific heat coefficient gamma (H) has been found in the low-temperature limit, which indicates that there is a nodal energy gap. Our analysis of the TF-mu SR results shows that the temperature dependence of the superfluid density is better described by a two-gap model either isotropic s + s wave or s + d wave than a single-gap isotropic s-wave model for the superconducting gap, consistent with other Fe-based superconductors. The combination of gamma(H) and TF-mu SR results suggest that the (s + d)-wave model is the most consistent candidate for the gap structure of ThFeAsN. The observation of two gaps in ThFeAsN suggests a multiband nature of the superconductivity possibly arising from the d bands of Fe ions. Furthermore, from our TF-mu SR study we have estimated the magnetic penetration depth in the polycrystalline sample of lambda(L) (0) = 375 nm, superconducting carrier density ns = 4.97x10(27) m(-3), and carrier's effective-mass m* = 2.48m(e). We compare the results of our present paper with those reported for the Fe-pnictide families of superconductors.