Nanoscopic coexistence of magnetism and superconductivity in YBa2Cu3O6+x   detected by MuSR
  We performed zero and transverse field MuSR experiments on a large number of YBa2Cu3O6+x samples. We detect coexistence of antiferro-type (AF) short range magnetism with superconductivity below T_f~10 K in compositions 0.37<x<0.39. Most muons experience local AF fields, even when SQUID detects a full SC 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. 
S. Sanna, G. Allodi, G. Concas, A. H. Hillier, R. De Renzi