Nuclear wave function interference in single-molecule electron transport

TL;DR

This paper investigates how charge-dependent vibrational potential changes in molecules cause interference effects in electron transport, revealing new phenomena like conductance anti-resonances and transport suppression.

Contribution

It introduces a model accounting for vibrational potential shifts and distortions due to charging, highlighting their impact on electron tunneling and interference effects in molecular devices.

Findings

Distortion breaks spectral symmetry and alters vibrational distributions.

Nuclear wave function interference causes conductance anti-resonances.

Coherent transport suppression occurs under specific conditions.

Abstract

It is demonstrated that non-equilibrium vibrational effects are enhanced in molecular devices for which the effective potential for vibrations is sensitive to the charge state of the device. We calculate the electron tunneling current through a molecule accounting for the two simplest qualitative effects of the charging on the nuclear potential for vibrational motion: a shift (change in the equilibrium position) and a distortion (change in the vibrational frequency). The distortion has two important effects: firstly, it breaks the symmetry between the excitation spectra of the two charge states. This gives rise to new transport effects which map out changes in the current-induced non-equilibrium vibrational distribution with increasing bias voltage. Secondly, the distortion modifies the Franck-Condon factors for electron tunneling. Together with the spectral asymmetry this gives rise to pronounced nuclear wave function interference effects on the electron transport. For instance nuclear-parity forbidden transitions lead to differential conductance anti-resonances, which are stronger than those due to allowed transitions. For special distortion and shift combinations a coherent suppression of transport beyond a bias voltage threshold is possible.