Theory of Fano resonance in single molecule electroluminescence induced by a scanning tunneling microscope

TL;DR

This paper presents a theoretical model explaining Fano resonance in single molecule electroluminescence induced by STM, highlighting the role of exciton-plasmon coupling and tip-molecule interactions.

Contribution

It introduces a nonequilibrium Green's function model to analyze Fano resonance and the influence of tip-molecule coupling on emission spectra, unifying experimental observations.

Findings

Fano resonance arises from coherent exciton-plasmon interaction.

Tip-molecule coupling significantly affects the emission spectrum.

The model explains various experimental phenomena.

Abstract

The coupling between molecular exciton and gap plasmons plays a key role in single molecular electroluminescence induced by a scanning tunneling microscope (STM). But it has been difficult to clarify the complex experimental phenomena. By employing the nonequilibrium Green's function method, we propose a general theoretical model to understand the light emission spectrum from single molecule and gap plasmons from an energy transport point of view. The coherent interaction between gap plasmons and molecular exciton leads to a prominent Fano resonance in the emission spectrum. We analyze the dependence of the Fano line shape on the system parameters, based on which we provide a unified account of several recent experimental observations. Moreover, we highlight the effect of the tip-molecule electronic coupling on the spectrum, which has hitherto not been considered.