Self-consistent theory of molecular switching

TL;DR

This paper develops a self-consistent theoretical model for a molecular switch with vibrational degrees of freedom, analyzing how electron transport influences switching dynamics and current-voltage characteristics under various conditions.

Contribution

It introduces a self-consistent approach to model the interplay between electron transport and vibrational states in molecular switches, including effects of environmental dissipation.

Findings

Transport voltage accelerates switching by driving the molecule out of thermal equilibrium.

Effective temperature of tunneling electrons depends on applied voltage, affecting switching dynamics.

Dissipative environments can suppress switching and introduce nonlinear transport behaviors.

Abstract

We study the model of a molecular switch comprised of a molecule with a soft vibrational degree of freedom coupled to metallic leads. In the presence of strong electron-ion interaction, different charge states of the molecule correspond to substantially different ionic configurations, which can lead to very slow switching between energetically close configurations (Franck-Condon blockade). Application of transport voltage, however, can drive the molecule far out of thermal equilibrium and thus dramatically accelerate the switching. The tunneling electrons play the role of a heat bath with an effective temperature dependent on the applied transport voltage. Including the transport-induced "heating" selfconsistently, we determine the stationary current-voltage characteristics of the device, and the switching dynamics for symmetric and asymmetric devices. We also study the effects of an extra dissipative environment and demonstrate that it can lead to enhanced non-linearities in the transport properties of the device and dramatically suppress the switching dynamics.