Charge Puddles in Graphene Near the Dirac Point

TL;DR

This study uses scanning tunneling microscopy to observe how charge puddles in graphene grow near the Dirac point, revealing inhomogeneities that affect electronic properties and are explained by screening theory.

Contribution

First direct microscopic observation of charge puddle growth in graphene near the Dirac point, linking spatial inhomogeneities to transport properties through screening theory.

Findings

Charge puddles increase in size and amplitude near the Dirac point.

Microscopic observations align with self-consistent screening theory.

Charge disorder impacts graphene's electronic behavior.

Abstract

The charge carrier density in graphene on a dielectric substrate such as SiO$_2$ displays inhomogeneities, the so-called charge puddles. Because of the linear dispersion relation in monolayer graphene, the puddles are predicted to grow near charge neutrality, a markedly distinct property from conventional two-dimensional electron gases. By performing scanning tunneling microscopy/spectroscopy on a mesoscopic graphene device, we directly observe the puddles' growth, both in spatial extent and in amplitude, as the Dirac point is approached. Self-consistent screening theory provides a unified description of both the macroscopic transport properties and the microscopically observed charge disorder.