Nonequilibrium electron-vibration coupling and conductance fluctuations in a C60-junction

TL;DR

This study uses first-principles calculations to explore how nonequilibrium electron-vibration interactions influence conductance fluctuations and bond formation in a C60 molecular junction, revealing polarity-dependent effects.

Contribution

It introduces a model linking nonequilibrium effects and vibrational heating to conductance fluctuations, highlighting the role of electron-vibration coupling in molecular electronics.

Findings

Strong coupling between C60 motion and electronic structure at contact formation

Polarity-dependent shifts in voltage drop and conductance fluctuations

Explanation of experimental conductance fluctuations via a nonequilibrium model

Abstract

We investigate chemical bond formation and conductance in a molecular C60-junction under finite bias voltage using first-principles calculations based on density functional theory and nonequilibrium Green's functions (DFT-NEGF). At the point of contact formation we identify a remarkably strong coupling between the C60-motion and the molecular electronic structure. This is only seen for positive sample bias, although the conductance itself is not strongly polarity dependent. The nonequilibrium effect is traced back a sudden shift in the position of the voltage drop with a small C60-displacement. Combined with a vibrational heating mechanism we construct a model from our results that explain the polarity-dependent two-level conductance fluctuations observed in recent scanning tunneling microscopy (STM) experiments [N. N\'eel et al., Nano Lett. 11, 3593 (2011)]. These findings highlight the significance of nonequilibrium effects in chemical bond formation/breaking and in electron-vibration coupling in molecular electronics.