Magnetoresistance in Disordered Graphene: The Role of Pseudospin and Dimensionality Effects Unraveled

TL;DR

This study uses advanced simulations to explore how pseudospin influences magnetoresistance in disordered graphene, revealing size-dependent effects and complex phase behavior in magnetoconductance.

Contribution

It provides a detailed theoretical analysis of pseudospin effects on magnetotransport in large-scale graphene models, including nanoribbons, using a novel computational approach.

Findings

Valley mixing causes positive magnetoconductance in 2D graphene.

Reducing disorder leads to weak antilocalization in large systems.

Nanoribbons do not show weak antilocalization effects.

Abstract

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 computational method, and simulating the effect of charges trapped in the oxide, different magnetoconductance fingerprints are numerically obtained in system sizes as large as 0.3 micronmeter squared, 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 a negative magnetoconductance (weak antilocalization) are obtained by reducing disorder strength down to the ballistic limit. In sharp contrast, graphene nanoribbons with lateral size as large as 10nm 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 some new light on the microscopical origin of pseudospin effects.