Charge Transport and Inhomogeneity near the Charge Neutrality Point in Graphene

TL;DR

This study investigates charge transport in graphene near the neutrality point, revealing inhomogeneous electron-hole regions and quantum Hall puddles through magnetic field-dependent resistivity measurements.

Contribution

It provides experimental evidence supporting the inhomogeneous electron-hole model and observes quantum Hall puddles in graphene at low temperatures and high magnetic fields.

Findings

Enhanced rho_xx(H) near neutrality point

Suppressed rho_xy(H) indicating electron-hole balance

Saturation of rho_xx(H) to ~h/e^2 at high fields

Abstract

The magnetic field-dependent longitudinal and Hall components of the resistivity rho_xx(H) and rho_xy(H) are measured in graphene on silicon dioxide substrates at temperatures from 1.6 K to room temperature. At charge densities near the charge-neutrality point rho_xx(H) is strongly enhanced and rho_xy(H) is suppressed, indicating nearly equal electron and hole contributions to the transport current. The data are inconsistent with uniformly distributed electron and hole concentrations (two-fluid model) but in excellent agreement with the recent theoretical prediction for inhomogeneously distributed electron and hole regions of equal mobility. At low temperatures and high magnetic fields rho_xx(H) saturates to a value ~h/e^2, with Hall conductivity << e^2/h, which may indicate a regime of localized v = 2 and v = -2 quantum Hall puddles.