Midgap states in doped Mott insulators in infinite dimensions

Doping of Mott insulators is analyzed in the mean-field-like limit of large lattice coordination or high dimensions. In this limit, it is demonstrated analytically that doping a Mott insulator induces states in the Mott-Hubbard gap, resulting in a narrow peak in the spectral density well separated, for weak doping, from the Hubbard bands. The energy at which this feature appears the critical chemical potential for doping is calculated as a function of U. It is also shown that the criteria for linear instability of the insulating Mott phase are the equality of chemical potential and the band edge. The nonlinear instability analyzed here always occurs strictly before the chemical potential reaches the band edge.