Current-induced mechanical torque in chiral molecular rotors

TL;DR

This paper introduces a classical model showing that chiral molecular rotors can be driven by current-induced torque without angular momentum transfer, leading to directed rotation above a threshold current.

Contribution

It presents a new mechanism for driving molecular rotors via current-induced torque in chiral systems, independent of angular momentum transfer.

Findings

Chiral molecular rotors undergo directed motion when current exceeds a threshold.

Rotation frequency is proportional to the ratio of charge carrier mass to helix mass.

The model predicts rotation driven by current in systems with an easy axis of rotation.

Abstract

A great endeavor has been undertaken to engineer molecular rotors operated by an electrical current. A frequently met operation principle is the transfer of angular momentum taken from the incident flux. In this paper we present an alternative driving agent that works also in situations where angular momentum of the incoming flux is conserved. This situation arises typically with molecular rotors that exhibit an easy axis of rotation. For quantitative analysis we investigate here a classical model, where molecule and wires are represented by a rigid curved path. We demonstrate that in the presence of chirality the rotor generically undergoes a directed motion, provided that the incident current exceeds a threshold value. Above threshold, the corresponding rotation frequency (per incoming particle current) for helical geometries turns out to be $2\pi m/M_1$, where $m/M_1$ is the ratio of the mass of an incident charge carrier and the mass of the helix per winding number.