Coexistence of magnetism and superconductivity in the pnictide high temperature superconductor SmO$_{0.82}$F$_{0.18}$FeAs measured by muon spin rotation

Abstract

Muon-spin rotation experiments were performed on a pnictide high temperature superconductor SmO$_{0.82}$F$_{0.18}$FeAs with a transition temperature of $T_{\rm c}$=45(3) K. A complex interplay of magnetic and superconducting behavior was observed which demonstrates the distinct role played by slow fluctuations of the magnetic moments of Sm and most likely also Fe. Notably, an unusual temperature dependent enhancement of these magnetic correlations was seen in the superconducting state. An estimate of the in-plane penetration depth $\lambda_{ab}(0)=184(15)$\thinspace nm was also obtained, which confirms that the pnictide superconductors obey an Uemura-style relationship between $T_{\mathrm{c}}$ and $\lambda_{ab}(0)^{-2}$.