Electron transport through a diatomic molecule

TL;DR

This paper investigates electron transport in diatomic molecules using NEGF theory, revealing interference effects that suppress conductance in bonding states and enhance it in anti-bonding states, with unique symmetric cases showing simplified conductance features.

Contribution

It provides explicit calculations of current and conductance in diatomic molecular junctions, highlighting interference effects and their impact on transport properties, including symmetric energy level cases.

Findings

Constructive interference enhances anti-bonding conductance.

Destructive interference suppresses bonding conductance.

Symmetric energy levels lead to single conductance peaks.

Abstract

Electron transport through a diatomic molecular tunnel junction shows wave like interference phenomenon. By using Keldysh non-equilibrium Green's function (NEGF) theory, we have explicitly presented current and differential conductance calculation for a diatomic molecular and two isolated atoms (two atoms having zero hybridization between their energy orbital) tunnel junctions. In case of a diatomic molecular tunnel junction, Green's function propagators entering into current and differential conductance formula interfere constructively for a molecular anti-bonding state and destructively for bonding state. Consequently, conductance through a molecular bonding state is suppressed, and to conserve current, conductance through anti-bonding state is enhanced. Therefore, current steps and differential conductance peaks amplitude show asymmetric correspondence between molecular bonding and anti-bonding states. Interestingly, for a diatomic molecule, comprising of two atoms of same energy level, these propagators interfere completely destructively for molecular bonding state and constructively for molecular anti-bonding state. Hence under such condition, a single step or a single peak is shown up in current versus voltage or differential conductance versus voltage studies.