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Fractional Chern insulators in magic-angle twisted bilayer graphene
Yonglong Xie1,2, Andrew T Pierce3, Jeong Min Park4
1Department of Physics, Harvard University, Cambridge, MA, USA. yxie1@g.harvard.edu.
Nature
|December 16, 2021
Summary
Fractional Chern insulators (FCIs) were observed in magic-angle twisted bilayer graphene. These findings suggest FCIs may be realized at zero magnetic field, enabling exploration of anyonic excitations.
Area of Science:
- Condensed Matter Physics
- Topological Matter
Background:
- Fractional Chern insulators (FCIs) are lattice analogues of fractional quantum Hall states.
- Theoretical studies predicted FCIs in systems with flat Chern bands and specific quantum geometry.
- Previous FCI observations required very large magnetic fields, hindering zero-field realization.
Purpose of the Study:
- To investigate the potential of magic-angle twisted bilayer graphene for realizing zero-field Fractional Chern Insulators.
- To explore the role of quantum geometry and magnetic fields in FCI emergence.
Main Methods:
- High-resolution local compressibility measurements.
- Utilizing magic-angle twisted bilayer graphene to host flat Chern bands at zero magnetic field.
- Applying low magnetic fields to tune Berry curvature.
Main Results:
- Observation of eight FCI states in magic-angle twisted bilayer graphene at low magnetic fields (starting at 5 T).
- Simultaneous disappearance of nearby topologically trivial charge density wave states.
- Demonstration that weak magnetic fields redistribute Berry curvature to favor FCI emergence.
Conclusions:
- Magic-angle twisted bilayer graphene provides a promising platform for realizing zero-field FCIs.
- The findings pave the way for manipulating anyonic excitations in flat moiré Chern bands.
- This research suggests FCIs can be achieved without extremely high magnetic fields.
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