Nanoscopic Coexistence of Magnetism and Superconductivity inYBa2Cu3O6+xDetected by Muon Spin Rotation

We performed zero and transverse field muon spin rotation experiments on a large number of ${\mathrm{Y}\mathrm{B}\mathrm{a}}_2{\mathrm{C}\mathrm{u}}_3{\mathrm{O}}_{6+x}$ samples. We detect the coexistence of antiferromagnetic (AF) short range magnetism with superconductivity below $T_f\lesssim 10\mathrm{K}$ in compositions $0.37\lesssim x\lesssim 0.39$. Most muons experience local AF fields, even when a SQUID detects a full superconducting volume fraction, which points to a local minimal interference organization of short AF stripes embedded in the superconductor. A detailed phase diagram is produced and the consequences of the minimal interference are discussed.