Quantum Hall effect in polycrystalline graphene: The role of grain boundaries
Résumé
We use numerical simulations to predict peculiar magnetotransport fingerprints in polycrystalline graphene,driven by the presence of grain boundaries of varying size and orientation. The formation of Landau levelsis shown to be restricted by the polycrystalline morphology, requiring the magnetic length to be smaller thanthe average grain radius. The nature of localization is also found to be unusual, with strongly localized statesat the center of Landau levels (including the usually highly robust zero-energy state) and extended electronicstates lying between Landau levels. These extended states percolate along the network of grain boundaries,resulting in a finite value for the bulk dissipative conductivity and suppression of the quantized Hall conductance.Such breakdown of the quantum Hall regime provoked by extended structural defects is also illustrated throughtwo-terminal Landauer-B ̈uttiker conductance calculations, indicating how a single grain boundary induces crosslinking between edge states lying at opposite sides of a ribbon geometry.