Fano Interference between a STM Tip and Mid Gap States in Graphene

TL;DR

This paper investigates how Fano interference affects STM measurements of mid-gap states in graphene, revealing how tip proximity can cause characteristic dips in the tunneling current due to hybridization effects.

Contribution

It demonstrates the occurrence of Fano hybridization between substrate resonances and STM tip conduction states, specifically in the context of graphene mid-gap states caused by defects or adsorbates.

Findings

Fano interference can cause dips in STM signals at certain energies.

Mid-gap states in graphene are susceptible to Fano hybridization effects.

Tip-surface distance influences the strength of Fano interference.

Abstract

We analyze the STM current through electronic resonances on a substrate as a function of tip-surface distance. We show that when the tip approaches the surface a Fano hybridization can occur between the electronic resonance on the substrate and the continuum of conduction states in the STM tip. A maximum of the density of states of the electronic resonance at some energy can then lead to a dip of the STM signal $dI/dV$. Resonances in graphene, known as mid gap states, are good candidates to produce this type of Fano interference. The mid gap states can be produced by local defects or adsorbates and we analyze the cases of top and hollow configurations of adsorbates.