Coherent laser control of the current through molecular junctions

TL;DR

This paper demonstrates how external laser fields can coherently control and suppress electron tunneling in molecular junctions, enabling ultrafast optical switching of current with potential applications in molecular electronics.

Contribution

It shows that coherent destruction of tunneling can be achieved in molecular junctions using time-dependent fields, extending previous work to include tunneling between a single site and reservoirs.

Findings

Current can be completely suppressed at specific field parameters.

Photon-assisted tunneling causes steps in current-voltage characteristics.

Laser pulses can be used for ultrafast optical switching.

Abstract

The electron tunneling through a molecular junction modeled by a single site weakly coupled to two leads is studied in the presence of a time-dependent external field using a master equation approach. In the case of small bias voltages and high carrier frequencies of the external field, we observe the phenomenon of coherent destruction of tunneling, i.e. the current through the molecular junction vanishes completely for certain parameters of the external field. In previous studies the tunneling within isolated and open multi-site systems was suppressed; it is shown here that the tunneling between a single site and electronic reservoirs, i.e. the leads, can be suppressed as well. For larger bias voltages the current does not vanish any more since further tunneling channels participate in the electron conduction and we also observe photon-assisted tunneling which leads to steps in the current-voltage characteristics. The described phenomena are demonstrated not only for monochromatic fields but also for laser pulses and therefore could be used for ultrafast optical switching of the current through molecular junctions.