Coherent laser control of the current through molecular junctions

¹  School of Engineering and Science, Jacobs University Bremen (Formerly International University Bremen.) - Campus Ring 1, 28759 Bremen, Germany
²  Institut für Physik, Technische Universität Chemnitz - 09107 Chemnitz, Germany

Received: 21 March 2007
Accepted: 6 June 2007

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.