Formation of the $n=0$ Landau level in hybrid graphene

Abstract

The minimum of 4-terminal conductance occurring at its charge neutral point has proven to be a robust empirical feature of graphene, persisting with changes to temperature, applied magnetic field, substrate, and layer thickness, though the theoretical mechanisms involved in transport about this point -- vanishing density of states, conventional band gap opening, and broken symmetry quantum Hall mobility gaps -- vary widely depending on the regime. In this paper, we report on observations of a regime where the 4-terminal conductance minimum ceases to exist: transport in monolayer graphene connected to bilayer graphene during the onset of the quantum Hall effect. As monolayer and bilayer graphene have distinct zero-energy Landau levels that form about the charge neutral point, our observations suggest that competitions between the differing many-body orderings of these states as they emerge may underlie this anomalous conductance.