Competing Zero-Field Chern Insulators in Superconducting Twisted Bilayer Graphene

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Phenomena

Background:

• Magic angle twisted bilayer graphene exhibits diverse superconducting, magnetic, and topological phases.
• Understanding these phases is crucial for advancing quantum electronics.

Purpose of the Study:

• To investigate the zero-field states in h-BN nonaligned twisted bilayer graphene devices at odd integer filling factors.
• To characterize the magnetic and superconducting properties and their transitions.

Main Methods:

• Utilized h-BN nonaligned twisted bilayer graphene devices.
• Observed the anomalous Hall effect near moiré cell filling factor ν=+1.
• Applied perpendicular magnetic fields to study phase transitions.

Main Results:

• Identified zero-field states as symmetry-broken Chern insulators with a Curie temperature of approximately 4.5 K.
• Observed a transition from Chern number C=±1 to C=3 in a magnetic field (B>0.5 T), evidenced by a quantized Hall plateau (Ryx=h/3e²).
• Revealed strong superconducting phases with critical temperatures up to 3.5 K.

Conclusions:

• Interaction-induced symmetry breaking leads to competing Chern insulator ground states.
• States with higher Chern numbers exhibit stronger coupling to magnetic fields.
• Demonstrated gate-induced transitions between magnetic and superconducting phases, a significant advancement for quantum electronics.