Coexistence of static magnetism and superconductivity in SmFeAsO1−xFx as revealed by muon spin rotation

The recent observation of superconductivity with critical temperatures (Tc) up to 55K in the pnictide RFeAsO1−xFx, where R is a lanthanide, marks the first discovery of a non-copper-oxide-based layered high-Tc superconductor1–3. It has raised the suspicion that these new materials share a similar pairing mechanism to the cuprate superconductors, as both families exhibit superconductivity following charge doping of a magnetic parent material. In this context, it is important to follow the evolution of the microscopic magnetic properties of the pnictides with doping and hence to determine whether magnetic correlations coexist with superconductivity. Here, we present a muon spin rotation study on SmFeAsO1−xFx, with x = 0–0.30 that shows that, as in the cuprates, static magnetism persists well into the superconducting regime. This analogy is quite surprising as the parent compounds of the tw