Muon spin relaxation studies of superconducting cuprates

The wide range of important insights into high- superconducting cuprates gained using the technique of muon spin relaxation is reviewed. As a probe of field inhomogeneity, transverse-field provides measurements of absolute penetration depths and evidence of pair breaking in overdoped cuprates, proximity-induced superconductivity, d-wave symmetry in the superconducting order parameter and vortex dimensionality cross-over in the highly anisotropic cuprates. Zero-field has revealed the presence of local moments and the coexistence of magnetism and superconductivity near the metal - insulator transition arising from phase separation. These results underscore the extraordinarily complex nature of the cuprates.