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Published on: July 24, 2015
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Symmetry-Broken Chern Insulators in Twisted Double Bilayer Graphene
Minhao He1, Jiaqi Cai1, Ya-Hui Zhang2
1Department of Physics, University of Washington, Seattle, Washington 98195, United States.
Nano Letters
|November 20, 2023
Summary
Twisted double bilayer graphene (tDBG) reveals a hierarchy of correlated and topological states. A novel symmetry-broken Chern insulator (SBCI) state emerges near optimal twist angles, showing spontaneous time-reversal symmetry breaking.
Area of Science:
- Condensed matter physics
- Materials science
- Quantum phenomena
Background:
- Twisted double bilayer graphene (tDBG) is a tunable platform for exploring strongly correlated and topological electronic states.
- Flat bands in tDBG can be modulated by displacement fields and twist angles, enabling precise control over material properties.
Purpose of the Study:
- To construct a comprehensive phase diagram of correlated and topological states in tDBG.
- To identify and characterize novel electronic states as a function of twist angle and displacement field.
Main Methods:
- Fabrication and electrical measurement of over a dozen tDBG devices.
- Systematic variation of twist angle and perpendicular displacement field.
- Analysis of symmetry-broken states, including Chern insulators.
Main Results:
- A hierarchy of symmetry-broken states emerges as the twist angle approaches approximately 1.34°.
- Discovery of a symmetry-broken Chern insulator (SBCI) state at 7/2 band filling and an incipient SBCI state at 11/3 filling.
- Observation of anomalous Hall effect at zero field in SBCI states, indicating spontaneous time-reversal symmetry breaking.
Conclusions:
- The phase diagram reveals a rich landscape of correlated and topological phenomena in tDBG.
- SBCI states represent a significant finding, with implications for understanding spontaneous symmetry breaking in moiré systems.
- The observed zero-field anomalous Hall effect suggests potential for novel spintronic applications and moiré superlattice physics.
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