Orbitally Controlled Quantum Hall States in Decoupled Two-Bilayer Graphene Sheets

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Mechanics

Background:

• Quantum Hall effects are fundamental in understanding electron behavior in 2D materials.
• Bilayer graphene systems offer unique platforms for exploring electron-electron interactions and novel quantum states.

Purpose of the Study:

• To investigate integer and fractional quantum Hall states in twisted Bernal bilayer graphene.
• To explore the role of interlayer Coulombic interactions and orbital index in forming exotic quantum states.

Main Methods:

• Fabrication of a stacked bilayer graphene system with suppressed interlayer tunneling.
• Utilizing asymmetric gate voltages to tune electronic states and orbital mixing.
• Observing quantum Hall states through electrical transport measurements.

Main Results:

• Integer and fractional quantum Hall states were observed in twisted bilayer graphene.
• A Bose-Einstein condensate was detected at half-filling for orbital index 1, but not for index 0.
• An even denominator fractional quantum Hall state at total filling -3/2 was found in orbital mixed space.

Conclusions:

• The observed phenomena are attributed to strong interlayer Coulombic interactions and skyrmion/anti-skyrmion excitations.
• Asymmetric gating allows control over orbital states, enabling navigation in orbital mixed space.
• The findings suggest a novel edge reconstruction involving electrons and chiral p-wave composite fermions.