Ingap state in doped and undoped cuprates

Abstract

The dispersive electronic state emerging upon carrier-doping in cuprates, i.e., the so-called ingap state, is derived in the three-band and one-band Hubbard models by means of the exact diagonalization of finite-size clusters. The dispersive state near the charge transfer gap at half filling undergoes a strongly momentum-dependent transfer of the spectral weight by carrier doping, and evolves into the new ingap state at the edge of the gap with a free-electron-like dispersion characteristic of a large Fermi surface consistent with Luttinger's sum rule. It is shown that the extended Hubbard model with strong nearest-neighbor repulsive interaction, on the other hand, forms a small Fermi surface by carrier doping and provides a counter-example of the doped cuprates.