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Moiré Flat Bands in Twisted Double Bilayer Graphene
Fatemeh Haddadi1, QuanSheng Wu1,2, Alex J Kruchkov3
1Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
Nano Letters
|February 26, 2020
Summary
Twisted double bilayer graphene exhibits a significant energy gap due to intrinsic symmetric polarization. A magic angle reveals flat bands, a fundamental feature not dependent on external fields.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Quantum Mechanics
Background:
- Twisted double bilayer graphene (TDBG) is a complex four-layer material.
- Understanding its electronic properties is crucial for novel electronic applications.
Purpose of the Study:
- Investigate the electronic band structure of TDBG.
- Identify the origin of flat bands observed at specific twist angles.
- Explore the role of intrinsic symmetric polarization (ISP).
Main Methods:
- Ab initio band structure calculations.
- Tight-binding parametrization incorporating ISP.
- Lattice relaxation modeling.
- Continuum model development.
Main Results:
- A considerable energy gap at the charge-neutrality point attributed to ISP.
- Identification of a magic angle region with remarkably flat bands.
- These flat bands are gapped out even without external electric fields.
Conclusions:
- The magic angle phenomenon in TDBG is an intrinsic property.
- ISP plays a key role in creating the observed band gap and flat bands.
- TDBG shares fundamental characteristics with twisted bilayer graphene.
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