Density of states of doped Hubbard clusters

Abstract

Numerical results for the density of states to remove or add electrons to a finite Hubbard cluster are presented for both positive and negative on-site interactions. The behavior of the filling versus the chemical potential is discussed. At half filling there is a gap in the density of states. When the repulsive-U Hubbard model is doped spectral weight is transferred into the gap, and the chemical potential is found to move across the gap as one goes from electron to hole doping. We discuss the relationship of these results to experiment. For the negative-U Hubbard model, the chemical potential shifts continuously and lies in the middle of the superconducting gap.