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arxiv: 2607.01186 · v1 · pith:XXKQU2ASnew · submitted 2026-07-01 · ❄️ cond-mat.mtrl-sci · cond-mat.str-el

Observation of Flat Bands in Type-II Weyl Semimetal TaRhTe₄

Pith reviewed 2026-07-02 09:15 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci cond-mat.str-el
keywords flat bandsWeyl semimetalTaRhTe4ARPEStype-II Weyl semimetalvan der Waalsnoncentrosymmetric
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The pith

Flat bands near the chemical potential are observed in bulk TaRhTe4, a type-II Weyl semimetal.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper reports the presence of flat bands near the chemical potential in bulk TaRhTe4 using angle-resolved photoemission spectroscopy. This material is a noncentrosymmetric van der Waals type-II Weyl semimetal where flat bands are unusual. The flat bands were not predicted by density functional theory calculations. This provides a platform where nontrivial topology coexists with flat bands near the Fermi level in a bulk system. Sympathetic readers would care because this allows study of flat band effects on transport without relying on twisted layers.

Core claim

The authors claim that ARPES measurements on TaRhTe4 reveal flat bands near the chemical potential. These bands, not predicted by DFT, indicate that nontrivial topology can coexist with flat bands near the Fermi level in this bulk noncentrosymmetric van-der Waals type-II Weyl semimetal.

What carries the argument

Angle-resolved photoemission spectroscopy revealing flat bands near the chemical potential in TaRhTe4.

Load-bearing premise

The ARPES spectra capture the bulk flat bands without significant surface reconstruction or artifacts mimicking flat dispersion.

What would settle it

If ARPES or other measurements show that the bands are actually dispersive or the flatness is due to matrix element effects, the observation would be invalidated.

Figures

Figures reproduced from arXiv: 2607.01186 by Adam Kaminski, Andrew Eaton, Benjamin Schrunk, Harry Rankin, K. U. R. R. S. Rathnayaka, Lin-Lin Wang, Maxwell Doyle, Paul C. Canfield, Tyler J. Slade, Yevhen Kushnirenko.

Figure 1
Figure 1. Figure 1: The crystal structure and Brillouin zone of TaRhTe4. a The crystal structure of TaRhTe4. Because it is noncentrosymmetric and layered, there are two different surface terminations, labeled by A and B here. b The Brillouin zone of TaRhTe4. Previous work on TaRhTe4 includes density functional theory (DFT) studies of few-layer and bulk crys￾tals, identification of the Weyl points, growth and crystal structure… view at source ↗
Figure 2
Figure 2. Figure 2: Fermi surfaces of TaRhTe4. a,b DFT-calculated and ARPES Fermi surfaces for termination B. The green and purple icons show the theoretical momentum positions of the Weyl points. The green WP projections have chirality -1 and the purple WP projections have chirality +1. The squares depict WP projections with predicted energy 13 meV above EF , whereas the circles represent WP projections with energy 50 meV be… view at source ↗
Figure 3
Figure 3. Figure 3: DFT and ARPES comparison of several energy-momentum cuts near the WP locations on each termination. a-c DFT-calculated energy-momentum cuts through termination B. The purple arrows indicate the theoretical locations of the WPs. d-f ARPES-measured energy-momentum cuts through termination B. The white arrows are placed at the same location as the purple arrows in the DFT calculations. g-i DFT-calculated ener… view at source ↗
Figure 4
Figure 4. Figure 4: Flat bands in the Fermi surface of termination A. a FS of termination A, showing how the flat bands extend throughout most of the Brillouin zone. b,c,d Several energy-momentum cuts in which the flat bands are visible. The flat bands are shown by the white arrows. e EDCs of panel (b), focused on the area enclosed by the smaller white frame. f EDCs of panel (b) without offset. The individual EDCs are colored… view at source ↗
Figure 5
Figure 5. Figure 5: Comparison of cuts in each termination near the location of the flat bands a Termination B, where the lowercase roman numerals label the locations of the cuts shown in b i-iv. b Corresponding energy-momentum cuts. No flat bands are seen in termination B. c Termination A, which exhibits the flat bands. The lowercase roman numerals label the locations of the cuts shown in d i-iv. d Energy-momentum cuts at th… view at source ↗
read the original abstract

Flat bands have been theoretically predicted for decades but have only recently been realized in quantum materials such as magic-angle twisted bilayer graphene, kagome and Lieb lattices, and rare-earth metal compounds. To date, only twisted layered materials have enabled tuning of flat-band energies near the electronic chemical potential, thereby influencing transport and thermodynamic properties. Here, we report the presence of flat bands near the chemical potential in bulk TaRhTe$_{4}$, a noncentrosymmetric van-der Waals type-II Weyl semimetal. Flat bands are rarely observed in Weyl semimetals, particularly in nonmagnetic bulk systems, and the observed flat bands were not predicted by density functional theory calculations. TaRhTe$_{4}$ therefore provides a platform in which nontrivial topology coexists with flat bands near the Fermi level, as evidenced by our angle-resolved photoemission spectroscopy measurements.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 0 minor

Summary. The manuscript reports the observation via ARPES of flat bands near the chemical potential in bulk TaRhTe4, a noncentrosymmetric van der Waals type-II Weyl semimetal. These bands were not predicted by DFT and are presented as evidence that nontrivial topology can coexist with flat bands near EF in a nonmagnetic bulk system.

Significance. If the bulk assignment and flatness quantification hold, the result would be significant: flat bands near EF are rare in Weyl semimetals, and their presence in a vdW type-II system could open routes to studying topology-flat-band interplay in transport and thermodynamics without requiring twisted-layer engineering.

major comments (2)
  1. [Abstract] Abstract: The claim that the flat bands are bulk states is load-bearing for the central result, yet the text supplies no photon-energy-dependent data, kz mapping, or multiple-Brillouin-zone checks to exclude surface termination states or matrix-element suppression that can produce apparent flat dispersion in vdW materials.
  2. [Abstract] Abstract: No quantitative metric, fitting procedure, or resolution limit is given for establishing band flatness (e.g., dispersion slope < threshold or R^{2} of linear fit), so the strength of the 'flat band' assignment relative to possible artifacts cannot be evaluated.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their detailed and constructive report. The two major comments highlight important points regarding the assignment of the observed bands as bulk states and the quantitative characterization of their flatness. We address each below and will revise the manuscript to incorporate additional data and analysis where needed.

read point-by-point responses
  1. Referee: [Abstract] Abstract: The claim that the flat bands are bulk states is load-bearing for the central result, yet the text supplies no photon-energy-dependent data, kz mapping, or multiple-Brillouin-zone checks to exclude surface termination states or matrix-element suppression that can produce apparent flat dispersion in vdW materials.

    Authors: We agree that explicit confirmation of the three-dimensional bulk character is essential for the central claim. The current manuscript relies on the use of bulk single crystals and consistency with the overall band structure, but does not present photon-energy-dependent ARPES or kz dispersion maps. In the revised version we will add photon-energy scans across multiple Brillouin zones, extract kz dispersion, and discuss possible surface contributions and matrix-element effects to strengthen the bulk assignment. revision: yes

  2. Referee: [Abstract] Abstract: No quantitative metric, fitting procedure, or resolution limit is given for establishing band flatness (e.g., dispersion slope < threshold or R^{2} of linear fit), so the strength of the 'flat band' assignment relative to possible artifacts cannot be evaluated.

    Authors: We acknowledge that a quantitative definition of flatness was not provided. In the revised manuscript we will include a clear metric: linear fits to the observed dispersions near EF, the extracted slope (in eV Å), the experimental momentum and energy resolution, and the resulting bandwidth upper bound. This will allow direct evaluation of the flat-band character relative to resolution limits. revision: yes

Circularity Check

0 steps flagged

Purely observational report with no derivation or self-referential steps

full rationale

The manuscript is an experimental observation paper whose central claim is the direct reporting of flat bands near E_F in TaRhTe4 via ARPES measurements. No equations, parameter fitting, predictions, or theoretical derivations are present in the provided text. The result is not obtained by reducing any quantity to a fitted input or self-citation; it is presented as raw spectroscopic evidence. No load-bearing self-citations, uniqueness theorems, or ansatzes appear. The derivation chain is empty by construction, making the circularity score 0.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Claim rests on standard experimental interpretation of ARPES data as bulk bands and on the assumption that performed DFT calculations are representative of the material's electronic structure; no free parameters or new entities introduced.

axioms (1)
  • domain assumption ARPES spectra reflect the intrinsic bulk electronic band structure in van der Waals materials
    Invoked implicitly when reporting flat bands near chemical potential from photoemission measurements.

pith-pipeline@v0.9.1-grok · 5723 in / 1104 out tokens · 26345 ms · 2026-07-02T09:15:59.571609+00:00 · methodology

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