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Helical Topological Edge States in a Quadrupole Phase
Feng Liu1, Hai-Yao Deng2, Katsunori Wakabayashi1
1Department of Nanotechnology for Sustainable Energy, School of Science and Technology, Kwansei Gakuin University, Gakuen 2-1, Sanda 669-1337, Japan.
Physical Review Letters
|April 2, 2019
Summary
Researchers demonstrate topological helical edge states in a honeycomb lattice's electric quadrupole phase. This discovery enables generating these states without spin-orbital couplings, advancing topological materials research.
Area of Science:
- Condensed Matter Physics
- Topological Materials Science
- Crystallography
Background:
- Topological electric quadrupoles extend crystal polarization theory to higher orders.
- These quadrupoles support topological states localized at edges and corners.
- Pseudospin, derived from point group symmetry, offers a new degree of freedom.
Purpose of the Study:
- To investigate topological states in a quadrupole phase of a honeycomb lattice.
- To explore the role of pseudospin in generating topological states.
- To identify conditions for creating helical edge states without spin-orbital couplings.
Main Methods:
- Theoretical analysis of a quadrupole phase in a honeycomb lattice model.
- Utilizing pseudospin degree of freedom linked to point group symmetry.
- Investigating the influence of mirror and time-reversal symmetries.
Main Results:
- Topological helical edge states and pseudospin-polarized corner states emerge in the quadrupole phase.
- The emergence of these states is linked to the pseudospin degree of freedom.
- A general condition for helical edge states is the presence of mirror or time-reversal symmetry.
Conclusions:
- The study successfully demonstrates the generation of topological helical edge states in a quadrupole phase.
- Pseudospin and specific symmetries (mirror or time-reversal) are key to realizing these states.
- This work provides a novel pathway for creating topological helical edge states without relying on spin-orbital couplings.
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