Double Quantum Spin Hall Phase in Moiré WSe2
Kaifei Kang1, Yichen Qiu2, Kenji Watanabe3
1School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, United States.
Nano Letters
|November 7, 2024
Summary
Researchers discovered a novel Quantum Spin Hall (QSH) phase in twisted bilayer WSe2, exhibiting multiple helical edge states. This breakthrough challenges previous limitations in material science for topological insulators.
Area of Science:
- Condensed matter physics
- Materials science
- Topological matter
Background:
- Quantum Spin Hall (QSH) insulators feature topologically protected helical edge states.
- Achieving multiple edge state pairs is challenging due to spin mixing.
Purpose of the Study:
- To experimentally demonstrate a QSH phase with multiple helical edge state pairs.
- Investigate the transport properties of these states in twisted bilayer WSe2.
Main Methods:
- Fabrication and characterization of twisted bilayer WSe2.
- Transport measurements at various Moiré hole filling factors (ν = 2 and 4).
- Magnetic field dependence studies (in-plane and out-of-plane).
Main Results:
- Observed nearly quantized resistance plateaus (within 10%) at ν = 2 and 4.
- Demonstrated large nonlocal transport consistent with helical edge states.
- Bulk remained insulating, with resistance showing unique magnetic field dependencies.
Conclusions:
- Experimental evidence for a QSH phase with one and two pairs of helical edge states in twisted bilayer WSe2.
- Results align with theoretical models of quantum transport in high spin Chern bands.
- Ising spin conservation symmetry plays a key role in protecting these states.
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