GENERALIZED MEAN FIELD ENERGY SPECTRUM OF THE MODIFIED TWO-BAND HUBBARD MODEL IN CUPRATES

摘要

The effective two-band two-dimensional Hubbard model of the high-T_C superconductivity in cuprates, as recently modified to include appropriately the zero doping limit [Gh. Adam, S.Adam, Rom. Journ. Phys., 54, no. 9-10, 797-814 (2009)], is rigorously solved within the generalized mean field approximation of the equation of motion of the Green function matrix. The energy spectra, derived both for the normal state and the superconducting state, are finite over the whole available range of the doping, irrespective of the kind of doping (with holes or with electrons) of the cuprate system. The hopping-induced hybridization of the normal state energy levels is found to preserve the centre of gravity of the unhybridized levels. However, the hopping-induced hybridization of the superconducting state energy levels at a given momentum q inside the Brillouin zone displaces the centre of gravity of the hybridized normal levels. This is consistent with the overall displacement of the energy spectrum of the superconducting state as found from very precise optical measurements.