Itinerant and high-energy localized single-particle spectra in large-U$_d$ high-Tc cuprates

Abstract

A theory of the underlying metallic state of large-U d high-T c cuprates is presented starting from the covalent Cu-2O 3-band model associated with a sufficiently small copper occupancy. U d = ∞ is dealt by the slave fermion approach. Diagrammatic low order NCA theory in terms of the Cu-O hopping is supplemented with two independent slave particle chemical potentials which implement the U(1) local gauge invariance "at average", thus avoiding the mean-field approximations. The resulting hole spectra consist of itinerant and localized states. The itinerant states close to the Fermi level are coherent. They exhibit dichotomies, the copper/oxygen in real and the nodal/antinodal in reciprocal space. The localized states, related to random Cu-O "mixed valence" fluctuations within the CuO 2 unit cells, are incoherent and fall well away from the Fermi level. Consequently, Luttinger's band sum rule for the conduction band is broken. Comparison with IPES, ARPES and NQR data on NCCO, LSCO, Bi2201 and Bi2212 -in order of increasing correlations -leads to remarkable agreements considering that only three bare band parameters are involved.