Switching the current through molecular wires with Gaussian laser pulses

– The influence of Gaussian laser pulses on the transport through molecular wires is investigated within a tight-binding model for spinless electrons including correlation. Motivated by the phenomenon of coherent destruction of tunneling for monochromatic laser fields, situations are studied in which the maximum amplitude of the electric field fulfills the conditions for the destructive quantum effect. It is shown that, as for monochromatic laser pulses, the average current through the wire can be suppressed. For parameters of the model, which do not show a net current without any optical field, a Gaussian laser pulse can establish a temporary current. In addition, the effect of electron correlation on the current is investigated. Introduction. – In recent years many groups have been working on making the vision of molecular electronics reality [1, 2]. This bottom-up approach for electronic devices has certain advantages over standard top-down approaches which are mainly used these days. In molecular electronics the transport is through single molecules or molecular aggregates and has therefore to be treated quantum mechanically. This quantum nature makes it of course more complicated to determine, for example, the current-voltage characteristics than in classical theories. But at the same time a quantum treatment offers certain advantages and especially the possibility of constructive or destructive interference effects. In the current letter we focus on the electron transport through a molecular wire which is coupled to two leads acting as electron source and drain. Many theories of quantum transport utilize the non-equilibrium Green’s function approach [3] which is formally exact within the lead-wire coupling. But because of the dependence of Green’s functions on two time arguments it is rather difficult to determine the current without any further approximations, as for example, the wide-band limit. Another possible route is to treat the lead-wire coupling perturbatively and derive quantum master equations for the electron dynamics in the wire and the current through the wire [4–7]. In addition to the wire-lead coupling a laser field can be coupled to the wire and/or the leads. This would possibly allow for an ultrafast opto-electronic device. First experimental [8] and theoretical [4, 7] investigations in this direction have been performed. Most of the theoretical studies are based on a master equation approach since in this formalism allows easily to include time-dependent laser fields. For time-periodic fields the Floquet theory can be employed [4]. Recently the present authors derived a formalism which