Spatially resolving unconventional interface Landau quantization in a graphene monolayer-bilayer planar junction

TL;DR

This study uses high-resolution STM and STS to investigate the electronic properties of a graphene monolayer-bilayer junction in the quantum Hall regime, revealing unconventional Landau quantization behaviors at the interface.

Contribution

It provides the first spatially resolved observation of Landau quantization at a graphene monolayer-bilayer interface, highlighting unique quantum conductance phenomena.

Findings

Detection of monolayer Landau levels below charge neutrality point

Observation of bilayer Landau levels above charge neutrality point

Unconventional Landau quantization linked to edge state conductance

Abstract

Graphene hybrid planar structures consisting of two regions with different quantum Hall (QH) states exhibit unusual transport properties1-5, originating from chiral edge states equilibration at the interface of the two different regions6. Here we present a sub-nanometre-resolved scanning tunnelling microscopy (STM) and spectroscopy (STS) study of a monolayer-bilayer graphene planar junction in the QH regime. The atomically well-defined interface of such a junction allows us to spatially resolve the interface electronic properties. Around the interface, we detect Landau quantization of massless Dirac fermions, as expected in graphene monolayer, below the charge neutrality point Nc of the junction, whereas unexpectedly, only Landau quantization of massive Dirac fermions, as expected in graphene bilayer, is observed above the Nc. The observed unconventional interface Landau quantization arises from the fact that the quantum conductance across the interface is solely determined by the minimum filling factors (number of edge modes) in the graphene monolayer and bilayer regions of the junction6,7.