Electric transport through circular graphene quantum dots: Presence of disorder

TL;DR

This study theoretically examines electric transport in circular graphene quantum dots, highlighting how different types of disorder affect spectral and transport properties, with a focus on edge disorder maintaining sharper bound state peaks.

Contribution

It compares continuum Dirac and tight-binding models for graphene quantum dots and explores the effects of various disorder types on their electronic transport properties.

Findings

Edge disorder preserves sharp bound state peaks.

Bulk and ripple disorder broaden spectral features.

Spectral and transport properties are highly disorder-dependent.

Abstract

The electronic states of an electrostatically confined cylindrical graphene quantum dot and the electric transport through this device are studied theoretically within the continuum Dirac-equation approximation and compared with numerical results obtained from a tight-binding lattice description. A spectral gap, which may originate from strain effects, additional adsorbed atoms or substrate-induced sublattice-symmetry breaking, allows for bound and scattering states. As long as the diameter of the dot is much larger than the lattice constant, the results of the continuum and the lattice model are in very good agreement. We also investigate the influence of a sloping dot-potential step, of on-site disorder along the sample edges, of uncorrelated short-range disorder potentials in the bulk, and of random magnetic-fluxes that mimic ripple-disorder. The quantum dot's spectral and transport properties depend crucially on the specific type of disorder. In general, the peaks in the density of bound states are broadened but remain sharp only in the case of edge disorder.