Quantum Hall Effect, Screening and Layer-Polarized Insulating States in Twisted Bilayer Graphene

TL;DR

This study explores how dual gating in twisted bilayer graphene allows independent control of electronic states, revealing Landau level crossings, inter-layer screening effects, and insulating states linked to edge phenomena.

Contribution

It demonstrates independent layer control in twisted bilayer graphene and characterizes inter-layer screening and insulating states using magnetotransport measurements.

Findings

Independent control of layer filling factors via dual gates.

Identification of Landau level crossings between layers.

Observation of insulating states at zero filling factor.

Abstract

We investigate electronic transport in dual-gated twisted bilayer graphene. Despite the sub-nanometer proximity between the layers, we identify independent contributions to the magnetoresistance from the graphene Landau level spectrum of each layer. We demonstrate that the filling factor of each layer can be independently controlled via the dual gates, which we use to induce Landau level crossings between the layers. By analyzing the gate dependence of the Landau level crossings, we characterize the finite inter-layer screening and extract the capacitance between the atomically-spaced layers. At zero filling factor, we observe magnetic and displacement field dependent insulating states, which indicate the presence of counter-propagating edge states with inter-layer coupling.