Controlling currents through molecular wires

Abstract

We investigate the possibility of controlling by means of external laser fields both the current through molecular wires and the corresponding noise properties. It is found that an appropriate off-resonant driving field reduces the coherent transport across the molecule resulting in a strong current suppression. The relative level of transport noise, characterized by a Fano factor, exhibits characteristic maxima and minima near regimes of current suppression. In a three-terminal configuration, the field allows one to steer the current selectively towards one terminal.

Coherently controlled molecular junctions

“…1 can be analyzed in terms of two competing Rabi oscillations: The field driven oscillations between the HOMO and LUMO of the donor (m = 0, 1) induced by the external laser field and the bridge mediated tunneling (superexchange) oscillations between the LUMOs of the donor and acceptor. The field driven frequency is defined by the detuning of the field from the donor resonance and the field intensity, 1 = (ε 1 − ε 0 − ω E ) 2 + (2 μE 0 ) 2 /¯, while the intra-molecular frequency is defined by the donor-acceptor level mismatch and the effective electronic coupling, 43 Figure 3 shows numerical simulations of current induced by CW laser for the model (2)-(5) treated within the mapping to a stationary problem (10). Current is shown as a function of the external field parameters: intensity ( Fig.…”

“…Here we seek not only charge pumping but also path selectivity during pumping, controlled by the external excitation. We start our consideration from the effective steady-state model (defined by the transformation (10) and the rotating wave approximation) applied to the Hamiltonian (11)- (14). The "standard" parameters as in the charge pump calculations with the donor-acceptor coupling are used here, where the electronic coupling between the donor LUMO and sites 3 and 4 (see Fig.…”

“…Bias across the junction, gate potential, optical excitation, magnetic field, and temperature gradient were considered in the literature as possible external controls for such devices. [8][9][10] The small size of molecules implies necessity of quantum mechanical treatment and naturally poses questions regarding the role of interference effects in the response of molecular electronic devices. Indeed, quantum coherence was recently found to prevail in nature's molecular systems, designed for performing electron 11 and energy transfer.…”

Coherence in charge and energy transfer in molecular junctions

“…(9) and (10). The starting points are expressions for charge and energy (phononassisted) fluxes within the nonequilibrium Green functions (NEGF) technique.…”

“…7,8 Coherent control of transport in molecular junctions is one of the focuses of research in this field. [9][10][11][12][13][14] Another focus is the dynamics of energy transfer between plasmonic and molecular excitations. [15][16][17][18][19] The importance of quantum coherence in energy transfer was demonstrated recently in studies of the initial stages of photosynthesis.…”