Charge-memory polaron effect in molecular junctions

TL;DR

This paper investigates the charge-memory effect in molecular junctions, demonstrating how electron-vibron interactions influence spontaneous and controlled switching behaviors, with implications for molecular electronics.

Contribution

It introduces a minimal polaron model to analyze charge-memory effects, revealing how bias voltage and junction symmetry affect switching dynamics and stability.

Findings

Spontaneous switching is exponentially suppressed at zero bias with strong electron-vibron interaction.

Asymmetric junctions enable hysteretic behavior and controlled switching.

Switching timescales can be tuned by changing the bias voltage.

Abstract

The charge-memory effect, bistability and switching between charged and neutral states of a molecular junction, as observed in recent STM experiments, is considered within a minimal polaron model. We show that in the case of strong electron-vibron interaction the rate of spontaneous quantum switching between charged and neutral states is exponentially suppressed at zero bias voltage but can be tuned through a wide range of finite switching timescales upon changing the bias. We further find that, while junctions with symmetric voltage drop give rise to random switching at finite bias, asymmetric junctions exhibit hysteretic behavior enabling controlled switching. Lifetimes and charge-voltage curves are calculated by the master equation method for weak coupling to the leads and at stronger coupling by the equation-of-motion method for nonequilibrium Green functions.