Quantum transport in chemically functionalized graphene at high magnetic field: Defect-Induced Critical States and Breakdown of Electron-Hole Symmetry

TL;DR

This study investigates how chemical functionalization of graphene with oxygen affects its quantum Hall transport properties at high magnetic fields, revealing defect-induced critical states and a breakdown of electron-hole symmetry.

Contribution

It uncovers the formation of defect-induced critical states and suggests a new type of zero-energy Hall plateau unrelated to Landau level degeneracy lifting.

Findings

Electron-hole symmetry is broken by oxygen adsorption.

Critical states form due to defect networks.

A potential new zero-energy Hall plateau is observed.

Abstract

Unconventional magneto-transport fingerprints in the quantum Hall regime (with applied magnetic field from one to several tens of Tesla) in chemically functionalized graphene are reported. Upon chemical adsorption of monoatomic oxygen (from 0.5% to few percents), the electron-hole symmetry of Landau levels is broken, while a double-peaked conductivity develops at low-energy, resulting from the formation of critical states conveyed by the random network of defects-induced impurity states. Scaling analysis hints towards the existence of an additional zero-energy quantized Hall conductance plateau, which is here not connected to degeneracy lifting of Landau levels by sublattice symmetry breakage. This singularly contrasts with usual interpretation, and unveils a new playground for tailoring the fundamental characteristics of the quantum Hall effect.