Nonequilibrium-Green’s-function theory of transport in interacting quantum dots

We present an approach for modeling nonequilibrium steady-state transport in quantum dots with interacting electrons, which employs real-time many-body Green’s functions on a tight-binding basis and accounts for dot-lead coupling exactly. This real-time Green’s-function description of transport is used to investigate the steady-state charge-density and current-voltage characteristics of one- and two-dimensional quantum dots having interacting electrons. The quantum dots are composed of a rectangular lattice of tight-binding sites, allowing for multiple degrees of freedom and a spatially varying external electric field. We investigate the effects of both the dot-lead coupling strength and finite current flowing in the dot. Our results indicate that as dot-lead coupling is increased, the Coulomb blockade disappears smoothly; furthermore, the Coulomb blockade may persist even in dots which have tunnel-junction resistances less than h/${\mathit{e}}^2$. We also find that in the Coulomb-blockade regime under conditions of current flow, the assumption of integer steady-state charge on the dot does not necessarily hold true, although the effect of single-electron tunneling does.