Nanoscopic coexistence of magnetism and Superconductivity in YBa2Cu 3O6+x detected by muon spin rotation

We performed zero and transverse field muon spin rotation experiments on a large number of YBa2Cu3O6x samples. We detect the coexistence of antiferromagnetic (AF) short range magnetism with superconductivity below Tf & 10 K in compositions 0:37 & x & 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.