Physics of a disordered Dirac point in epitaxial graphene from temperature-dependent magnetotransport measurements

We report a study of disorder effects on epitaxial graphene in the vicinity of the Dirac point by magnetotransport. Hall effect measurements show that the carrier density increases quadratically with temperature, in good agreement with theoretical predictions which take into account intrinsic thermal excitation combined with electron-hole puddles induced by charged impurities. We deduce disorder strengths in the range 10.2--31.24.pt0exmeV, depending on the sample treatment. We investigate the scattering mechanisms and estimate the impurity density to be 3.0--9.1×10¹⁰4pt0excm^-2 for our samples. A scattering asymmetry for electrons and holes is observed and is consistent with theoretical calculations for graphene on SiC substrates. We also show that the minimum conductivity increases with increasing disorder strength, in good agreement with quantum-mechanical numerical calculations.