Charge transport and inhomogeneity near the minimum conductivity point in graphene

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 1.6 K <= T <= 300 K. At charge densities near the minimum conductivity point rho(xx)(H) is strongly enhanced and rho(xy)(H) is suppressed, indicating nearly equal electron and hole contributions to the current. The data are inconsistent with the standard two-fluid model but consistent with the prediction for inhomogeneously distributed electron and hole regions of equal mobility. At low T and high H, rho(xx)(H) saturates to a value similar to h/e(2), with Hall conductivity << e(2)/h, which may indicate a regime of localized v=2 and v=-2 quantum Hall puddles.