Strong localization in a suspended monolayer graphene by intervalley scattering

TL;DR

This study demonstrates strong localization effects in suspended monolayer graphene caused by intervalley scattering, leading to insulating behavior and quantum Hall features at very low temperatures.

Contribution

It reveals the role of intervalley scatterers in inducing strong localization and insulating states in high-mobility suspended graphene.

Findings

Conductance drops from ~e^2/h at 30 K to ~0.01 e^2/h at 20 mK.

Observation of a direct insulator to quantum Hall transition within 0.4 T.

Presence of broken-symmetry quantum Hall plateaux at ν=0, ±1.

Abstract

A gate induced insulating behavior at zero magnetic field is observed in a high mobility suspended monolayer graphene near the charge neutrality point. The graphene device initially cleaned by a current annealing technique was undergone a thermo-pressure cycle to allow short range impurities to be adsorbed directly on the ultra clean graphene surface. The adsorption process generated a strong temperature and electric field dependent behavior on the conductance of the graphene device. The conductance around the neutrality point is observed to be reduced from around $e^2/h$ at 30 K to $\sim0.01~e^2/h$ at 20 mK. A direct transition from insulator to quantum Hall conductor within $\approx0.4~T$ accompanied by broken-symmetry-induced $\nu=0,\pm1$ plateaux confirms the presence of intervalley scatterers.