Competing ordered states with filling factor two in bilayer graphene

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Transport

Background:

• The quantum Hall effect (QHE) typically requires strong magnetic fields to quantize Hall conductivities in 2D materials.
• Time-reversal symmetry breaking can induce QHE-like phenomena even at zero magnetic field.
• Bilayer graphene exhibits competing broken symmetry states, some with quantized Hall conductivities.

Purpose of the Study:

• To investigate and stabilize broken symmetry states in charge-neutral bilayer graphene.
• To explore the nature of quantized Hall conductivities in these stabilized states.
• To elucidate the rich landscape of competing ordered states in bilayer graphene.

Main Methods:

• Stabilization of competing states in bilayer graphene using external magnetic and electric fields.
• Transport spectroscopy measurements to probe the electronic properties of the stabilized states.
• Analysis of Hall conductivities to identify quantization and symmetry properties.

Main Results:

• Two distinct broken symmetry states with two quantum units of Hall conductivity were stabilized.
• One state was stabilized by a large magnetic field, the other by a large electric field.
• The majority spins formed a quantum anomalous Hall state, while minority spins exhibited Kekulé or quantum valley Hall states.

Conclusions:

• External fields can stabilize exotic broken symmetry states in bilayer graphene with quantized Hall conductivities.
• These findings demonstrate the existence of multiple competing ordered states in bilayer graphene.
• The study provides insights into the complex interplay of symmetry, topology, and electronic order in graphene systems.