Formation of the n = 0 Landau level in hybrid graphene

The minimum of 4-terminal conductance occurring as carrier density is tuned through 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. This observed increase in conductance is accompanied by decreases in conductance at the half-filling of the Landau levels adjacent to the charge-symmetric, zero-energy level. As monolayer and bilayer graphene have distinct zero-energy 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 these anomalous conductances. (letter)