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This paper addresses the long standing and controversial issue of the originof superconductivity in cuprates. Their superconductivity can be attributed toamphoteric defects associated with vacancy sites in copper oxide planes. Alocal defect lattice relaxation results in a negative-$U$ energy binding twoholes on amphoteric defects in the donor configuration that act as preformedboson pair. Thermodynamic equilibrium between defects in the donor and acceptorconfigurations stabilizes Fermi energy at the amphoteric defect chargetransition state assuring resonant coupling between free holes and thelocalized hole pairs. Model calculations show that the critical temperature isprimarily determined by the density of the amphoteric defects in the donorconfiguration, explaining the ubiquity of dome-like dependence of the criticaltemperature on the doping as well as its universal dependence on the superfluiddensity. Intentional doping with chemical acceptors or donors is neithernecessary nor sufficient condition for superconductivity that is fullydetermined by the amphoteric defects whose concentration can be controlled bycrystal nonstoichiometry. The only role of chemical doping is changing thebalance between concentrations of amphoteric defects in the donor and acceptorconfigurations resulting in an increase of the superfluid density and thus alsothe critical temperature for acceptor and a decrease for donor doping. Thisaccounts for the experimentally observed distinct asymmetry between the domestructures for the chemical doping with acceptors and donors. The unusualsensitivity of the critical temperature to external perturbations is explainedby the resonant nature of the coupling between free holes and preformed holepairs. The work has broader implications as it could be applicable to othersuperconductors with dome-like dependence of the critical temperature ondoping.

Possible Origin of Preformed Hole Pairs and Superconductivity in Cuprates