Lifting the Franck-Condon blockade in driven quantum dots

TL;DR

This paper explores how a time-dependent oscillatory drive can lift the Franck-Condon blockade in quantum dots, significantly increasing current by exciting vibrons, using perturbative and master equation approaches.

Contribution

It demonstrates that oscillatory gate voltages can overcome Franck-Condon blockade, a novel control mechanism for electron transport in quantum dots.

Findings

Drive lifts the Franck-Condon blockade by exciting vibrons.

Relative current change grows exponentially with drive strength.

Both perturbation theory and master equation approaches agree on the effect.

Abstract

Electron-vibron coupling in quantum dots can lead to a strong suppression of the average current in the sequential tunneling regime. This effect is known as Franck-Condon blockade and can be traced back to an overlap integral between vibron states with different electron numbers which becomes exponentially small for large electron-vibron coupling strength. Here, we investigate the effect of a time-dependent drive on this phenomenon, in particular the effect of an oscillatory gate voltage acting on the electronic dot level. We employ two different approaches: perturbation theory based on nonequilibrium Keldysh Green's functions and a master equation in Born-Markov approximation. In both cases, we find that the drive can lift the blockade by exciting vibrons. As a consequence, the relative change in average current grows exponentially with the drive strength.