Anomalous current-electric field characteristics in transport through a nanoelectromechanical systems

A deep understanding of the correlation between electronic and mechanical degrees of freedom is crucial to the development of quantum devices in a nanoelectromechanical system (NEMS). In this work, we first establish a fully quantum mechanical approach for transport through a NEMS device, which is valid for arbitrary bias voltages, temperatures, and electro-mechanical couplings. We find an anomalous current-electric field characteristics at a low bias, where the current decreases with a rising electric field, associated with the backward tunneling of electrons for a weak mechanical damping. We reveal that this intriguing behavior arises from a combined effect of mechanical motion and Coulomb blockade, where the rapid increase of backward tunneling events at a large oscillation amplitude suppresses the forward current due to prohibition of double occupation. In the opposite limit of strong damping, the oscillator dissipates its energy to the environment and relaxes to the ground state rapidly. Electrons then transport via the lowest vibrational state such that the net current and its corresponding noise have a vanishing dependence on the electric field.