Muon spin rotation studies of doping in high-T-c superconductors

Muon spin rotation studies on high temperature superconducting cuprates wil l be reviewed. After an introduction to the technique, studies on the super fluid density will be described and the universal variation of the superflu id density n(s) as a function of p will be presented. Important exceptions will be discussed, such as the YBa2Cu3O7-delta system, where, besides the i ntrinsically superconducting CuO2 planes, an interlayer may be metallised ( here the CuO chains) which consequently contributes to a significant enhanc ement in superfluid density and associated improvement in technologically i nteresting properties such as flux pinning and critical current density. Ev idence for an unconventional pairing state, possibly with d-wave symmetry, is presented from studies of the rapid suppression of superfluid density du e to the substitution of structural inhomogeneities (such as Zn) that intro duce strong scattering centers within the CuO2 planes. Finally, the phase d iagram of the antiferromagnetic correlations and, in particular, their coex istence with the superconducting state, will be discussed in terms of muon spin rotation experiments in zero external magnetic field.