On the nature of pseudogap anomalies in HTSC

Abstract

We proposed the model of HTSC where the interaction of electrons from oxygen band with the diatomic negative U-centers (NUC) on pairs of Cu ions in CuO2 plane is assumed to be responsible for the superconducting pairing. As follows from the model the occupation η of NUC with real electrons reduces superconducting order parameter due to decreasing of number of states available for scattering of electron pairs. The charge fluctuations between NUC and valence band will result in fluctuations of pairing interaction. In clusters, containing small number of NUC's, where the relative fluctuations of η are great enough, the superconducting gap may open at T*>Tc∞ and close at TC<TC∞, where Tc∞ is the temperature of superconducting transition for infinite cluster. The doping dependences of T* and Tc for YBa2Cu3O6+δ are calculated as two roots of the same square equation. The obtained results demonstrate the impressive agreement with experiment.