Muon Spin Rotation Studies of Doping in High-T$\text{}_{c}$ Superconductors

Muon spin rotation studies on high temperature superconducting cuprates will be reviewed. After an introduction to the technique, studies on the superfluid density will be described and the universal variation of the superfluid density n$\text{}_{s}$ as a function of p will be presented. Important exceptions will be discussed, such as the YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{7-δ}$ system, where, besides the intrinsically superconducting CuO$\text{}_{2}$ planes, an interlayer may be metallised (here the CuO chains) which consequently contributes to a significant enhancement in superfluid density and associated improvement in technologically interesting properties such as flux pinning and critical current density. Evidence for an unconventional pairing state, possibly with d-wave symmetry, is presented from studies of the rapid suppression of superfluid density due to the substitution of structural inhomogeneities (such as Zn) that introduce strong scattering centers within the CuO$\text{}_{2}$ planes. Finally, the phase diagram of the antiferromagnetic correlations and, in particular, their coexistence with the superconducting state, will be discussed in terms of muon spin rotation experiments in zero external magnetic field.