Isotope effects in HTS cuprates: pressure, anisotropy, impurities and pseudogap.

The oxygen isotope effect on Tc and the superfluid density in high-Tc superconductor cuprates has been investigated as a function of pressure, anisotropy, impurity scattering and pseudogap correlations. The doping dependent effects observed are fully consistent with the calculated behaviour in the presence of scattering and depleted normal-state electronic density of states. Like so many other physical properties they reveal a critical doping state where the pseudogap abruptly closes.