Moiréless correlations in ABCA graphene

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Twisted van der Waals materials enable gate-tunable correlated phenomena via flat electronic bands.
• Moiré superlattices are typically required to induce these effects.

Purpose of the Study:

• To demonstrate emergent correlated phases in multilayer rhombohedral graphene without moiré superlattices.
• To investigate the electronic properties and potential applications of ABCA graphene.

Main Methods:

• Fabrication of small-angle twisted double-bilayer graphene.
• Scanning tunneling spectroscopy (STS) to probe electronic structure.
• Mean-field theoretical calculations for interaction modeling.

Main Results:

• Formation of large, uniform rhombohedral four-layer (ABCA) graphene regions.
• Observation of an ultra-sharp van Hove singularity (3-5 meV half-width) in ABCA graphene.
• Emergence of a correlated many-body gap (9.5 meV) at charge neutrality when the singularity crosses the Fermi level.
• Identification of potential excitonic insulator or ferrimagnetic states.
• Discovery of gate-tunable topological helical edge states at ABCA/ABAB graphene interfaces.

Conclusions:

• Small-angle twisted double-bilayer graphene provides a platform for correlated phenomena without moiré patterns.
• ABCA graphene hosts unique electronic states, including a significant many-body gap.
• This material system is a promising candidate for programmable topological quantum devices.