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Two-dimensional higher-order Weyl semimetals
by Lizhou Liu, Qing-Feng Sun, and Ying-Tao Zhang
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Submission summary
| Authors (as registered SciPost users): | Yingtao Zhang |
| Submission information | |
|---|---|
| Preprint Link: | scipost_202507_00076v1 (pdf) |
| Date submitted: | July 28, 2025, 10:30 a.m. |
| Submitted by: | Yingtao Zhang |
| Submitted to: | SciPost Physics |
| Ontological classification | |
|---|---|
| Academic field: | Physics |
| Specialties: |
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| Approach: | Theoretical |
Abstract
We propose a theoretical scheme to realize two-dimensional higher-order Weyl semimetals using a trilayer topological film coupled with a $d$-wave altermagnet. Our results show that the trilayer topological film exhibits two-dimensional Weyl semimetal characteristics with helical edge states. Notably, the Weyl points are located at four high-symmetry points in the Brillouin zone, and the topology of symmetric subspaces governs the formation of these Weyl points and edge states. Upon introducing a $d$-wave altermagnet oriented along the $z$-direction, gaps open in the helical edge states while preserving two Weyl points, leading to the realization of two-dimensional higher-order Weyl semimetals hosting topological corner states. The nonzero winding number in the subspace along the high-symmetry line serves as a topological invariant characterizing these corner states, and the other subspace Hamiltonian confirms the existence of the Weyl points. Finally, a topological phase diagram provides a complete topological description of the system.
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Report
The work is novel in extending higher-order topology to 2D gapless systems, leveraging altermagnets, a recently proposed magnetic order, for momentum-selective edge gapping while preserving bulk Weyl nodes. This "gapless-bulk, gapped-boundary" paradigm is intriguing and could inspire hybrid topological-magnetism studies. The subspace decomposition via algebraic symmetry M enables analytical invariants (Chern/winding numbers), providing clear topological classification. Numerical results (band structures, nanoflakes) consistently support claims.
A key weakness is the phenomenological nature: the Hamiltonian, while symmetry-guided, lacks tight-binding derivation from realistic materials, limiting experimental relevance (e.g., Bi2Se3 trilayers may not match exactly). The M symmetry is artificial (not crystal-derived), potentially over-idealized; its realizability in van der Waals structures needs justification. Logic is mostly consistent, but inconsistencies arise: Weyl points are claimed at high-symmetry points, yet 2D Weyl nodes typically require accidental crossings—verify if dispersions are truly linear (Fig. 2(a) suggests quadratic touches at some points). Altermagnet justification is perturbative but assumes uniform J; real proximity effects may vary. Phase diagram boundaries (|m0|=4/8|m1|) derive from subspace closures, but exclude J dependence—small J is stated not to affect it, yet Fig. 3 uses J=0.6, risking oversight for larger J. No discussion of disorder/interaction effects on corner states.
Advice for Improvement: Link model to specific materials (e.g., MnTe/Bi2Se3 interfaces) with ab initio estimates for parameters. Analytically derive corner state wavefunctions or use effective models for edges. Expand experimental probes: beyond STM, suggest transport (e.g., nonlocal resistance for corners) or ARPES for Weyl nodes. Address finite-size effects on hybridization. Revise for clarity: define "higher-order" explicitly in 2D context; add error bars or convergence checks for numerics.
The concept is innovative and timely, but requires stronger material ties and error checks for publication. I recommend major revisions.
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Author: Yingtao Zhang on 2025-12-05 [id 6107]
(in reply to Report 1 on 2025-11-04)We thank the referee for carefully reading our manuscript and the valuable report. We provide our response to the questions raised by the referee in the attached file.
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