Abstract
The d-p model with the local constraint has been studied. With help of the slave boson and 1/N-expansion the electronic states are investigated. At T < T0 (coherence temperature) a new band (mid-gap state) appears in the CT gap which behaves as the Fermi liquid with the large Fermi surface. Luttinger sum rule is proved. At T0≲T≲ω0 (resonance temperature) the mid-gap state behaves as the marginal Fermi liquid. At T≳ ω0 such renormalized band collapses. These occur as the crossover phenomena in contrast to the phase transition in the mean field approximation. The anomalous physical properties are observed in the temperature region of the marginal Fermi liquid. The system is metallic or insulating at non-doping limit when Δ̅=Δ/2tpd<2.37 or Δ̅>2.37. For Δ̅=2.37, the charge susceptibility becomes zero, which is a characteristic feature of the strongly correlated system. Upd changes the critical value of Δ̅, enhances the charge fluctuation and causes the phase separation. The interactions mediated by the enhanced charge fluctuation may derive the superconductivity of the cuprate compounds.
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