Imaging Universal Conductance Fluctuations in Graphene

TL;DR

This paper investigates conductance fluctuations in graphene, revealing how they depend on disorder, impurity motion, and proximity to the Dirac point, challenging the universality of these fluctuations in certain regimes.

Contribution

It provides the first extensive numerical analysis of conductance fluctuations in graphene, showing their suppression near the Dirac point and dependence on impurity motion and disorder strength.

Findings

CF are suppressed near the Dirac point in ballistic systems.

CF approach the universal value at strong disorder.

Single impurity motion causes conductance fluctuations of order e^2/h.

Abstract

We study conductance fluctuations (CF) and the sensitivity of the conductance to the motion of a single scatterer in two-dimensional massless Dirac systems. Our extensive numerical study finds limits to the predicted universal value of CF. We find that CF are suppressed for ballistic systems near the Dirac point and approach the universal value at sufficiently strong disorder. The conductance of massless Dirac fermions is sensitive to the motion of a single scatterer. CF of order $e^2/h$ result from the motion of a single impurity by a distance comparable to the Fermi wavelength. This result applies to graphene systems with a broad range of impurity strength and concentration while the dependence on the Fermi wavelength can be explored {\em via} gate voltages. Our prediction can be tested by comparing graphene samples with varying amounts of disorder and can be used to understand interference effects in mesoscopic graphene devices.