Pseudogaps in the three-band Hubbard model
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Using the strong coupling diagram technique, the energy spectrum of the three-band Hubbard model is investigated. In these calculations, the series in powers of the copper-oxygen hybridization for the irreducible part is approximated by two lowest-order terms. For parameters of hole-doped cuprates the calculated energy spectrum consists of lower and upper Hubbard subbands of predominantly copper nature, oxygen bands with some admixture of copper states and the Zhang-Rice states of mixed nature. The spectrum contains two pseudogaps, the lower of which separates the Hubbard subband from Zhang-Rice and oxygen bands. The pseudogaps arise due to multiple reabsorption of carriers in states with double occupancy of sites by holes or electrons.