Kinetic rectification of charge transmission through a single molecule

Based on the nonequilibrium density matrix method the kinetic description of electron transmission through a single molecule with delocalized molecular orbitals is accomplished. Analytic expressions for the sequential (hopping) component and the direct (tunnel) component of the current are derived and analyzed for the particular case where the transmission proceeds through a single molecular orbital. It is shown that the population of the orbital by the transferred electrons leads to the formation of two transmission channels. One channel is related to electron transmission through the molecule in a state without an extra (transferred) electron. The other channel accounts for electron transmission with the participation of the singly reduced state of the molecule. Because the absence of an extra electron or the presence of one or two extra electrons is determined by inelastic electron hopping processes, even the direct (tunnel) current through the molecule is controlled by inelastic processes. These processes lead to a specific kinetic rectification effect, including a regime with negative differential resistance, for the tunneling component of the current, provided that the hopping rates between the molecule and the left electrode strongly differ from the hopping rates related to the right electrode.