Electronic structure and excitation spectra in doped nickelates

We examine the electronic structure and the excitation spectra in two-dimen sional doped nickelates. The numerically exact diagonalization study on sma ll clusters for the Hubbard model with degenerate e(g) orbital bands are pe rformed. We find that the orbital dependence of the hopping matrix elements plays a crucial role in the electronic structure and the excitation spectr a. The optical conductivity at the filling of one electron per site is show n to exhibit a characteristic feature. (C) 2000 Elsevier Science B.V. All r ights reserved.