Coexistence of magnetic fluctuations and superconductivity in the pnictide high temperature superconductor SmFeAsO${}_{1-x}$F${}_x$ measured by muon spin rotation

Muon-spin rotation experiments were performed on the pnictide high temperature superconductor SmFeAsO${}_{1-x}$F${}_x$ with x=0.18 and 0.3. We observed an unusual enhancement of slow spin fluctuations in the vicinity of the superconducting which suggests that the spin fluctuations contribute to the formation of an unconventional superconducting state. An estimate of the in-plane penetration depth ${\lambda }_{ab}(0)=190(5)$\thinspace nm was obtained, which confirms that the pnictide superconductors obey an Uemura-style relationship between $T_{\mathrm{c}}$ and ${\lambda }_{ab}(0{)}^{-2}$.