12 Jul 2007
Researchers from Germany describe electron tunneling through a molecular junction in the presence of a time-dependent external field.
Applying an external time-dependent field, such as a laser field or an additional ac voltage, to a molecular junction generates effects such as photon-assisted tunneling (PAT) and coherent destruction of tunneling (CDT).
Professor Kleinekathöfer and colleagues have now used a master equation approach to model electron tunneling through a single-site molecular junction that is weakly coupled to two leads in the presence of a time-dependent external field (Europhys. Lett. 79 27006).
In the technique chosen by the researchers, the effect of the external field on the coupling between molecule and leads is treated exactly, and not neglected as in other theories. This makes it possible to examine the influence of the laser on this coupling.
The researchers found that CDT occurred in cases with small bias voltages and high carrier frequencies of the external field, with the current through the molecular junction vanishing completely for certain parameters of the external field. For larger bias voltages the current no longer vanishes as further tunneling channels participate in the electron conduction.
The researchers demonstrate the described phenomena not only for monochromatic fields but also for laser pulses, which may enable the development of ultrafast opto-electronic switches.