Multigap superconductivity in ThAsFeN investigated using μ SR 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-μSR) measurements. Our magnetization and heat-capacity measurements reveal an onset of bulk superconductivity with Tc∼30K. A nonlinear magnetic-field dependence of the specific heat coefficient γ(H) has been found in the low-temperature limit, which indicates that there is a nodal energy gap. Our analysis of the TF-μSR 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 γ(H) and TF-μSR 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-μSR study we have estimated the magnetic penetration depth in the polycrystalline sample of λL(0)=375nm, superconducting carrier density ns=4.97×1027m-3, and carrier's effective-mass m∗=2.48me. We compare the results of our present paper with those reported for the Fe-pnictide families of superconductors.