Quantum Transport and Field Induced Insulating States in Bilayer Graphene pnp Junctions

TL;DR

This study investigates quantum transport phenomena in high-quality bilayer graphene pnp junctions, revealing electric field-induced band gaps, variable range hopping behavior, and fractional quantum Hall states, highlighting potential for advanced electronic applications.

Contribution

It demonstrates electric field control of band gaps and insulating states in bilayer graphene, with detailed analysis of quantum Hall effects and transport mechanisms in pnp junctions.

Findings

Band gap opening with high On/Off ratio at zero magnetic field.

Exponential conductance decrease within the gap explained by variable range hopping.

Observation of fractional quantum Hall conductance and insulating states at high magnetic fields.

Abstract

We perform transport measurements in high quality bilayer graphene pnp junctions with suspended top gates. At a magnetic field B=0, we demonstrate band gap opening by an applied perpendicular electric field, with an On/Off ratio up to 20,000 at 260mK. Within the band gap, the conductance decreases exponentially by 3 orders of magnitude with increasing electric field, and can be accounted for by variable range hopping with a gate-tunable density of states, effective mass, and localization length. At large B, we observe quantum Hall conductance with fractional values, which arise from equilibration of edge states between differentially-doped regions, and the presence of an insulating state at filling factor {\nu}=0. Our work underscores the importance of bilayer graphene for both fundamental interest and technological applications.