Conductance response of graphene nanoribbons and quantum point contacts in the scanning probe measurements

TL;DR

This paper presents a theoretical analysis of how a scanning probe affects the conductance in graphene nanoribbons and quantum point contacts, revealing detailed local electronic responses and resonances.

Contribution

It introduces a comprehensive theoretical framework for understanding conductance responses in graphene nanostructures under scanning probe influence, including edge effects and localized resonances.

Findings

Formation of n-p junctions induced by the probe

Resolution of standing waves in asymmetric nanoribbons

Localized resonances in long constrictions causing conductance peaks

Abstract

We provide a theoretical study of the conductance response of systems based on graphene nanoribbon to the potential of a scanning probe. The study is based on the Landauer approach for the tight-binding Hamiltonian with an implementation of the quantum transmitting boundary method and covers homogenous nanoribbons, their asymmetric narrowing and quantum point contacts of various profiles. The response maps at low Fermi energies resolve formation of n-p junctions induced by the probe potential and a presence of zigzag-armchair segments of the edges for inhomogeneous ribbons. For an asymmetric narrowing of the nanoribbons the scanning probe resolves formation of standing waves related to backscattering within the highest subband of the narrower part of the system. The QPCs containing a long constriction support formation of localized resonances which induce a system of conductance peaks that is reentrant in the Fermi energy, with the form of the probability density that can be resolved by the conductance mapping. For shorter constrictions the probe induces smooth conductance minima within the constrictions. In general, besides the low-energy transport gap, in the wider parts of the ribbon the variation of the conductance of the system is low compared to the narrower part.