Magnetoresistance in disordered graphene: The role of pseudospin and dimensionality effects unraveled

We report a theoretical low-field magnetotransport study unveiling the effect of pseudospin in realistic models of weakly disordered graphene-based materials. Using an efficient Kubo simulation method, and simulating the effect of charges trapped in the oxide, different magnetoconductance fingerprints are numerically obtained for system sizes as large as 0.3 μm², containing tens of millions of carbon atoms. In two-dimensional graphene, a strong valley mixing is found to irreparably yield a positive magnetoconductance (weak localization), whereas crossovers from positive to negative magnetoconductance (weak antilocalization) are obtained by reducing the disorder strength down to the ballistic limit. In sharp contrast, graphene nanoribbons with lateral size as large as 10 nm show no sign of weak antilocalization, even for very small disorder strength. Our results rationalize the emergence of a complex phase diagram of magnetoconductance fingerprints, shedding new light on the microscopical origin of pseudospin effects.