Laser controlled molecular switches and transistors

Abstract

We investigate the possibility of optical current control through single molecules which are weakly coupled to leads. A master equation approach for the transport through a molecule is combined with a Floquet theory for the timedependent molecule. This yields an efficient numerical approach to the evaluation of the current through time-dependent nano-structures in the presence of a finite external voltage. We propose tunable optical current switching in two-and three-terminal molecular electronic devices driven by properly adjusted laser fields, i.e., a novel class of molecular transistors.

Transport Through a Driven Three-Site System

“…Depending on the nanosystem itself, laser fields or microwave radiation are appropriate for this purpose. As has been shown recently in a theoretical work [12], a switch can be obtained by applying a coherent monochromatic field. Moreover, it is even possible to control the corresponding noise level [13].…”

Controlling currents through molecular wires

“…2(a) depicts the dc current and the zero-frequency noise for a wire with equal onsite energies E n = 0 and a relatively large applied voltage. As a remarkable feature, we find that for certain values of the field amplitude A, the current drops to a value of some percent of the current in the absence of the field [24]. A perturbation theory for the Floquet equation (6) for ∆, Γ Ω yields that the driving results in a renormalized hopping matrix element ∆ → ∆ eff = J 0 (A/ Ω )∆, where J 0 denotes the zeroth-order Bessel function.…”

Molecular Wires in Electromagnetic Fields

“…The laser irradiation induces a large current enhancement of several orders of magnitude and also can reduce the current noise level. The observation of these resonances could serve as an experimental starting point for the more challenging attempt of measuring quantum ratchet effects [7,8] or current switching by laser fields [9,10].…”

“…This results in a directed electron transport even in the absence of any applied voltage [7,8]. Another theoretically predicted effect is the current suppression by the laser field [9,10] which offers the possibility to control both the average current and the current noise.Since the considered frequencies lie below typical plasma frequencies of metals, the laser light will be reflected at the metal surface, i.e., it does not penetrate the leads. Consequently, we assume that the leads' bulk properties are essentially unaffected by the laser field-in particular each lead remains close to equilibrium.…”

“…This results in a directed electron transport even in the absence of any applied voltage [7,8]. Another theoretically predicted effect is the current suppression by the laser field [9,10] which offers the possibility to control both the average current and the current noise.…”