Indexed on: 22 May '07Published on: 22 May '07Published in: Physics - Mesoscopic Systems and Quantum Hall Effect
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.