Quantum Hall Effects in Monolayer-Bilayer Graphene Planar Junctions

TL;DR

This study reveals unique quantum Hall effects at the interface of monolayer and bilayer graphene, showing quantized Hall resistance behaviors that depend on carrier type and magnetic field direction, explained by edge state chirality.

Contribution

It demonstrates the existence of novel quantum Hall states at SLG-BLG interfaces with asymmetries explained by edge state chirality and Landauer-Büttiker analysis.

Findings

Quantized Hall resistance switches between SLG and BLG states

Symmetry breaking in Hall resistance in hybrid structures

Edge state chirality determines interface quantum Hall states

Abstract

The Hall resistance of a homogeneous electron system is well known to be anti-symmetric with respect to the magnetic field and the sign of charge carriers. We have observed that such symmetries no longer hold in planar hybrid structures consisting of partly single layer graphene (SLG) and partly bilayer graphene (BLG) in the quantum Hall (QH) regime. In particular, the Hall resistance (R12xy) across the SLG and BLG interface is observed to exhibit quantized plateaus that switch between those characteristic of SLG QH states and BLG QH states when either the sign of the charge carriers (controlled by a back gate) or the direction of the magnetic field is reversed. Simultaneously reversing both the carrier type and the magnetic field gives rise to the same quantized Hall resistances. The observed SLG-BLG interface QH states, with characteristic asymmetries with respect to the signs of carriers and magnetic field, are determined only by the chirality of the QH edge states and can be explained by a Landauer-B\"uttiker analysis applied to such graphene hybrid structures involving two regions of different Landau level (LL) structures.