Effects of electronic correlations and magnetic field on a molecular ring out of equilibrium

We study effects of electron-electron interactions on the steady-state characteristics of a hexagonal molecular ring in a magnetic field, as a model for a benzene molecular junction. The system is driven out of equilibrium by applying a bias voltage across two metallic leads. We employ a model Hamiltonian approach to evaluate the effects of on-site as well as nearest-neighbour density-density type interactions in a physically relevant parameter regime. Results for the steady-state current, charge density and magnetization in three different junction setups (para, meta and ortho) are presented. Our findings indicate that interactions beyond the mean-field level renormalize voltage thresholds as well as current plateaus. Electron-electron interactions lead to substantial charge redistribution as compared to the mean-field results. We identify a strong response of the circular current on the electronic structure of the metallic leads. Our results are obtained by steady-state Cluster Perturbation Theory, a systematically improvable approximation to study interacting molecular junctions out of equilibrium, even in magnetic fields. Within this framework general expressions for the current, charge density and magnetization in the steady-state are derived. The method is flexible and fast and can straight-forwardly be applied to effective models as obtained from ab-initio calculations.