Current-induced dynamics in carbon atomic contacts

TL;DR

This paper develops a semi-classical Langevin approach combined with DFT to study current-induced vibrational dynamics and instabilities in atomic carbon chains connected to graphene electrodes, highlighting the role of non-conservative and Berry-phase forces.

Contribution

It introduces a novel Langevin-based method to predict device stability and explore current-induced vibrational effects in molecular-scale contacts with gate control.

Findings

Current-induced instabilities occur at realistic bias and gate voltages.

Gate voltage can control vibrational instabilities independently of bias.

Joule heating and anharmonic interactions are crucial for energy redistribution.

Abstract

The effect of electronic current on the atomic motion still poses many open questions, and several mechanisms are at play. Recently there has been focus on the importance of the current-induced non-conservative forces (NC) and Berry-phase derived forces (BP) regarding the stability of molecular-scale contacts. Systems based on molecules bridging electrically gated graphene electrodes may offer an interesting test-bed for these effects. We employ a semi-classical Langevin approach in combination with DFT calculations to study the current-induced vibrational dynamics of an atomic carbon chain connecting electrically gated graphene electrodes. This illustrates how the device stability can be predicted solely from the modes obtained from the Langevin equation including the current induced forces. We point out that the gate offers control of the current independent of bias voltage which can be used to explore current-induced vibrational instabilities due the NC/BP forces. Furthermore, using tight-binding and the Brenner potential we illustrate how Langevin-type molecular dynamics can be performed including the Joule heating effect for the carbon chain systems. Molecular dynamics including current-induced forces enables an energy redistribution mechanism among the modes, mediated by anharmonic interactions, which is found to be vital in the description of the electronic heating. We have developed a semi-classical Langevin equation approach which can be used to explore current-induced dynamics and instabilities. We find instabilities at experimentally relevant bias and gate voltages for the carbon chain system.