Special CPM Seminar

Transport through NEMS: semiclassical dynamics in the nonadiabatic regime

Anja Metelmann

Technische Universität Berlin

We compare the semiclassical description of nanoelectromechanical systems (NEMS) within and beyond the Born-Oppenheimer approximation.

NEMS enable the detailed study of the interaction between electrons, tunneling through a nano-scale device, and the degrees of freedom of a mechanical system.

We work in the semiclassical regime where an expansion around the classical path is performed. The advantage of this method is, that its nonperturbative in the system-lead coupling, because the exact electronic solutions are included. We develop a nonadiabatic approach, where we can treat the oscillator and the electrons on the same time scale without further constrains.

The considered NEMS models contain a single phonon (oscillator) mode linearly coupled to an electronic few-level system in contact with external particle reservoirs (leads). Using Feynman-Vernon influence functional theory, we derive a Langevin equation for the oscillator's trajectories. A stationary electronic current through the system generates nontrivial dynamical behaviour of the oscillator, even in the adiabatic regime. For the case of two coupled electronic levels, we discuss the differences between the adiabatic and the nonadiabatic regime of the oscillator dynamics. Additonally, we show that our nonadiabatic method is easily transferable to other kinds of (semiclassical) systems.