Unconventional fractional quantum Hall effect in bilayer graphene

Area of Science:

• Condensed Matter Physics
• Materials Science

Background:

• Recent advancements in Hall measurements enable precise observation of the fractional quantum Hall effect (FQHE) in bilayer graphene.
• Previous studies on suspended and boron nitride encapsulated samples provided foundational data.

Purpose of the Study:

• To investigate and explain newly observed FQHE features in bilayer graphene.
• To reconcile experimental findings with existing theoretical models, particularly the composite fermion model.

Main Methods:

• Utilizing experimental data from Hall measurements in open-face boron nitride encapsulated bilayer graphene samples.
• Applying a topological approach to model the FQHE hierarchy.

Main Results:

• Observed FQHE in multiple subbands (n=0, 1, 2) of the bilayer system.
• Identified FQHE features inconsistent with the conventional composite fermion model.
• Demonstrated a distinct FQHE hierarchy compared to monolayer graphene or GaAs 2DEG.

Conclusions:

• The conventional composite fermion model is insufficient to explain observed FQHE in bilayer graphene.
• A topological approach, incorporating inter-sheet electron hopping, successfully explains the FQHE hierarchy.
• The findings offer a new framework for understanding FQHE in two-dimensional electron systems.