Nanoscopic coexistence of magnetic and superconducting states within the FeAs layers of CeFeAsO1-xFx

We report on the coexistence of magnetic and superconducting states in CeFeAsO1-x F x for x=0.062, characterized by transition temperatures Tm =30 K and Tc =18 K, respectively. Zero-field and transverse-field muon-spin-relaxation measurements show that below 10 K the two phases coexist within a nanoscopic scale over a large volume fraction. This result clarifies the nature of the magnetic-to-superconducting transition in the CeFeAsO1-x F x phase diagram, by ruling out the presence of a quantum critical point which was suggested by earlier studies.