Coexistence of electron and hole transport in graphene

TL;DR

This paper demonstrates that both electrons and holes coexist in graphene near the charge neutrality point, revealing a quantum Hall metal state characterized by simultaneous electron and hole transport at high magnetic fields.

Contribution

It provides experimental evidence for the coexistence of electrons and holes in graphene and links this to the degeneracy of the zero-energy Landau level at high magnetic fields.

Findings

Both electrons and holes are present at the charge neutrality point.

Electron and hole concentrations increase with Landau level degeneracy.

A quantum Hall metal state at =0 is observed with coexisting carriers.

Abstract

When sweeping the carrier concentration in monolayer graphene through the charge neutrality point, the experimentally measured Hall resistivity shows a smooth zero crossing. Using a two- component model of coexisting electrons and holes around the charge neutrality point, we unambiguously show that both types of carriers are simultaneously present. For high magnetic fields up to 30 T the electron and hole concentrations at the charge neutrality point increase with the degeneracy of the zero-energy Landau level which implies a quantum Hall metal state at \nu=0 made up by both electrons and holes.