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

TL;DR

This paper investigates the disappearance of the conductance minimum at the charge neutral point in hybrid graphene systems, revealing complex interactions between monolayer and bilayer graphene Landau levels during quantum Hall effect onset.

Contribution

It reports the first observation of the loss of the conductance minimum in hybrid graphene, highlighting the role of competing many-body states in this phenomenon.

Findings

Conductance minimum disappears in hybrid graphene during quantum Hall onset

Distinct zero-energy Landau levels in monolayer and bilayer graphene influence transport

Competition between many-body orderings affects conductance behavior

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.