Current rectification in molecular junctions produced by local potential fields

TL;DR

This study demonstrates that local electric fields from an external charged probe can induce rectification in symmetric molecular junctions by creating quasi-local states that influence electron transport.

Contribution

It reveals how a local potential can turn a symmetric molecule into a diode by inducing quasi-local states affecting current flow.

Findings

A symmetric molecule can exhibit diode-like behavior under a local electric field.

The position of the charged probe influences the rectification effect.

Induced quasi-local states near the Fermi level are key to current asymmetry.

Abstract

The transport properties of a octane-dithiol (ODT) molecule coupled to Au(001) leads are analyzed using density functional theory and non-equilibrium Green functions. It is shown that a symmetric molecule can turn into a diode under influence of a local electric field created by an external charged probe. The origin of the asymmetry of the current--voltage ($I-V$) dependence is traced back to the appearance of a probe induced quasi--local state in the pseudogap of the ODT molecule. The induced state affects electron transport, provided it is close to the Fermi level of the leads. An asymmetric placement of the charged probe along the alkane chain makes the induced quasi--local state in the energy gap very sensitive to the bias voltage and results in rectification of the current. The results based on DFT are supported by independent calculations using a simple one--particle model Hamiltonian.