Physical mechanism for a kinetic energy driven zero-bias anomaly in the Anderson-Hubbard model

The combined effects of strong disorder, strong correlations, and hopping in the Anderson-Hubbard model have been shown to produce a zero-bias anomaly which has an energy scale proportional to the hopping and minimal dependence on interaction strength, disorder strength, and doping. Disorder-induced suppression of the density of states for a purely local interaction is inconsistent with both the Efros-Shklovskii Coulomb gap and the Altshuler-Aronov anomaly, and moreover the energy scale of this anomaly is inconsistent with the standard energy scales of both weak- and strong-coupling pictures. We demonstrate that a density of states anomaly with similar features arises in an ensemble of two-site systems, and we argue that the energy scale t emerges in strongly correlated systems with disorder due to the mixing of lower and upper Hubbard orbitals on neighboring sites.