Experimental Observation of Surface States and Landau Levels Bending in Bilayer Graphene

TL;DR

This study uses STM and STS to investigate the electronic surface states and Landau level behavior at edges of bilayer graphene, revealing edge-localized states and Landau level bending indicative of quantum Hall edge states.

Contribution

It provides direct experimental evidence of surface states at zigzag edges and Landau level evolution into edge states in bilayer graphene using microscopic techniques.

Findings

Zero-energy peak localized at zigzag edges

Landau levels bend near edges in magnetic field

Evidence of quantum Hall edge states in bilayer graphene

Abstract

We report on microscopic measurements of the low-energy electronic structures both at zigzag and armchair edges of bilayer graphene using scanning tunneling microscopy and spectroscopy (STM and STS). We have found that, both in the absence and in the presence of a magnetic field, an almost zero-energy peak in density of states was localized at zigzag edges, as expected for the surface states at zigzag edges of bilayer graphene. In the quantum Hall regime, we have observed clearly Landau levels bending away from the charge neutrality point near both the zigzag and armchair edges. Such a result is a direct evidence for the evolution of Landau levels into the quantum Hall edge states in graphene bilayers. Our experiment indicates that it is possible to explore rich quantum Hall physics in graphene systems using STM and STS.