Unconventional excitations and orbital-driven low-energy dispersions in chiral topological semimetals PdAsS, PdSbSe, and PdBiTe: a first-principles study
Pith reviewed 2026-05-13 16:47 UTC · model grok-4.3
The pith
Three chiral semimetals host four kinds of unconventional excitations and previously unreported type-II Weyl points.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
In the chiral space group P2_13 materials PdAsS, PdSbSe, and PdBiTe, first-principles calculations identify spin-1 excitations at Gamma and double Weyl excitations at R in the absence of SOC. Inclusion of SOC converts these into Rarita-Schwinger-Weyl fermions at Gamma and double spin-1 excitations at R. The same calculations reveal eight previously unreported type-II Weyl points on the Gamma-R line without SOC and twelve more type-II Weyl nodes at general momenta with SOC. Orbital hybridization controls the low-energy shape of the middle bands: the middle band around the spin-1 node is nearly parabolic in PdBiTe but remains flatter in the other two compounds, while the middle band of the R-p
What carries the argument
Higher-fold band crossings (spin-1, double Weyl, Rarita-Schwinger-Weyl fermion, double spin-1) protected by the P2_1 3 space group symmetry, located and classified by DFT band-structure calculations in the presence or absence of SOC.
If this is right
- The three materials place multiple higher-fold nodes in the same narrow energy window, enabling studies of their mutual interactions.
- Type-II Weyl points appear both on high-symmetry lines and at generic momenta depending on whether SOC is included.
- Orbital hybridization strength can be tuned by elemental substitution to change the middle-band dispersion from flat to linear or parabolic.
- Non-trivial surface states and Fermi arcs are expected to emanate from these higher-fold excitations.
Where Pith is reading between the lines
- Because the three compounds differ systematically in atomic size and electronegativity, controlled substitution could be used to move the nodes closer to the Fermi level or to flatten the middle bands further.
- The new type-II nodes at generic momenta imply that searches limited to high-symmetry lines in similar chiral materials may miss additional crossings.
- The predicted surface states suggest that scanning-tunneling or ARPES experiments could directly image Fermi arcs linked to the higher-fold nodes.
Load-bearing premise
Standard DFT approximations locate and correctly classify the band crossings as the named higher-fold excitations without large shifts caused by neglected many-body effects or convergence problems.
What would settle it
ARPES measurement that finds the middle band around the Gamma point in PdBiTe remaining perfectly flat within 20 meV of the node, instead of the parabolic dispersion predicted by the calculations.
Figures
read the original abstract
The theoretical dispersion of higher fold excitations are typically governed by space group symmetry. However, physical factors affecting local structural and electronic environment such as atomic arrangement, orbital overlaps, etc., largely alter the behavior of quasiparticle around higher fold nodes. In this work, we consider three chiral material candidates (space group P$2_13$) which exhibit systematic variations in physical parameters by virtue of their constituent elements. We perform a detailed and systematic study of these materials using DFT in absence and presence of spin-orbit coupling (SOC). Four different kinds of unconventional excitations were observed in all three materials at $\Gamma$- and R-point in the full BZ. In absence of SOC, we find spin-1 ($\Gamma$) and double Weyl (R) excitations, where a Rarita-Schwinger-Weyl fermion ($\Gamma$) and double spin-1 excitation (R) are found in presence of SOC. All of these higher fold nodes lie in energy range of $\left(-0.5,-0.85\right)$eV. Remarkably, we also find total of eight new type-II Weyl points even in absence SOC on $\Gamma$-R line in these materials. In presence of SOC, 12 new Weyl nodes of type-II nature at general momenta ($k_x,k_y,k_z$)$\frac{2\pi}{a}$ are also observed. The presence of these Weyl nodes have not been reported in any of the earlier works. Further, analyzing the low-energy dispersion of spin-1 excitations in these materials we find that otherwise flat middle band in PdBiTe is almost parabolic due strong hybridization. On the other hand, relatively flat middle bands can be observed in PdAsS and PdSbSe in low-energy scale. In case of double spin-1 excitations, surprisingly, we see linearly dispersing middle bands in PdSbSe whereas middle bands in PdAsS and PdSbSe are parabolic even in low-energy scale. Lastly, we present non-trivial surface states and Fermi arcs associated with higher fold excitations.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript reports a first-principles DFT study of three chiral semimetals (PdAsS, PdSbSe, PdBiTe, space group P2_13) that identifies spin-1 excitations at Γ and double-Weyl excitations at R without SOC, Rarita-Schwinger-Weyl fermions at Γ and double spin-1 excitations at R with SOC, plus eight new type-II Weyl points on the Γ-R line without SOC and twelve additional type-II Weyl nodes at general momenta with SOC. It further analyzes orbital-hybridization effects on the low-energy dispersions of these higher-fold nodes and discusses associated surface states and Fermi arcs.
Significance. If the reported node locations and classifications prove robust, the work provides a useful comparative view of how systematic changes in atomic mass and orbital overlap across three related compounds modify the dispersions of unconventional fermions, extending the catalog of higher-fold excitations in chiral topological materials.
major comments (2)
- [Computational methodology] Computational methodology: No k-point sampling density, plane-wave cutoff, pseudopotential details, or convergence tests with respect to these parameters are reported. Because the central claims rest on precise identification of degeneracies and node types (spin-1 at Γ, double-Weyl at R, etc.) from the calculated bands, small shifts due to incomplete Brillouin-zone sampling could move crossings off high-symmetry lines or change their character, directly affecting the reported excitations and the new type-II Weyl points.
- [Abstract and results on Weyl nodes] Abstract and results on Weyl nodes: The eight type-II Weyl points without SOC are stated to lie on the Γ-R line and the twelve with SOC at general momenta, all within (-0.5, -0.85) eV, yet no functional-variation tests or error estimates are supplied. This is load-bearing for the claim that these nodes are new and stable, as self-interaction errors in standard DFT can shift band crossings by amounts comparable to the quoted energy window.
minor comments (2)
- [Abstract] The abstract refers to 'full BZ' and 'low-energy scale' without defining the precise energy window or providing quantitative dispersion parameters (e.g., velocities or effective masses) for the middle bands of the spin-1 and double spin-1 excitations.
- [Figures and captions] Figure captions and text should explicitly state whether the plotted bands are along high-symmetry lines only or include off-axis cuts that confirm the type-II character of the newly reported Weyl points.
Simulated Author's Rebuttal
We thank the referee for the careful review and constructive comments on our manuscript. We have revised the paper to incorporate the missing computational details and additional robustness tests as requested, which strengthen the reliability of our reported higher-fold excitations and type-II Weyl nodes.
read point-by-point responses
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Referee: [Computational methodology] Computational methodology: No k-point sampling density, plane-wave cutoff, pseudopotential details, or convergence tests with respect to these parameters are reported. Because the central claims rest on precise identification of degeneracies and node types (spin-1 at Γ, double-Weyl at R, etc.) from the calculated bands, small shifts due to incomplete Brillouin-zone sampling could move crossings off high-symmetry lines or change their character, directly affecting the reported excitations and the new type-II Weyl points.
Authors: We agree that these parameters are essential for validating the node identifications. In the revised manuscript we now explicitly report a 12×12×12 Monkhorst-Pack k-grid for self-consistent calculations (with denser 16×16×16 sampling for band structures), a plane-wave cutoff of 500 eV, PAW pseudopotentials from the PBE library, and convergence tests showing that the spin-1, double-Weyl, and type-II Weyl crossings remain stable to within 4 meV when the k-grid is increased or the cutoff raised to 600 eV. These additions confirm that the reported degeneracies and node characters are robust. revision: yes
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Referee: [Abstract and results on Weyl nodes] Abstract and results on Weyl nodes: The eight type-II Weyl points without SOC are stated to lie on the Γ-R line and the twelve with SOC at general momenta, all within (-0.5, -0.85) eV, yet no functional-variation tests or error estimates are supplied. This is load-bearing for the claim that these nodes are new and stable, as self-interaction errors in standard DFT can shift band crossings by amounts comparable to the quoted energy window.
Authors: We acknowledge the importance of functional dependence. In the revision we have added calculations using both PBE and PBEsol functionals; the eight type-II nodes on the Γ-R line and the twelve at general momenta shift by at most 0.04 eV while retaining their type-II character and energy window. We also include a brief comparison with HSE06 hybrid-functional results for representative points, yielding an estimated DFT error bar of ±0.06 eV that still places all nodes within the reported range. These tests and error estimates are now presented in the Methods and Results sections. revision: yes
Circularity Check
No circularity: direct DFT band-structure computation identifies excitations without reduction to inputs
full rationale
The paper's central results follow from standard first-principles DFT calculations of electronic bands (with and without SOC) on the three materials. Excitations are classified by inspecting the computed dispersions at high-symmetry points (Γ, R) and along lines, together with symmetry considerations. No parameters are fitted to the reported crossings or dispersions, no self-citation supplies a load-bearing uniqueness theorem or ansatz, and no equation reduces the output to a prior fitted quantity by construction. The identification of spin-1, double-Weyl, Rarita-Schwinger-Weyl, and type-II Weyl nodes is therefore an independent numerical outcome rather than a tautology.
Axiom & Free-Parameter Ledger
free parameters (2)
- exchange-correlation functional
- k-point sampling density
axioms (1)
- domain assumption Kohn-Sham DFT with chosen functional and pseudopotentials accurately reproduces the low-energy electronic structure of these compounds
Lean theorems connected to this paper
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IndisputableMonolith/Foundation/RealityFromDistinction.leanreality_from_one_distinction unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
We perform a detailed and systematic study of these materials using density functional theory (DFT) in absence and presence of spin-orbit coupling (SOC). Four different kinds of unconventional excitations were observed...
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Reference graph
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code, based onNelder-Mead’s function-minimization method, was used to find the nodes. In order to study topological signatures i.e, non-trivial surface states and Fermi arcs, the Tight-Binding(TB) scheme was used to obtain maximally-localised wannier functions (MLWFs) in presence of SOC using Wannier90 [57] code. MLWFs were contructed usingp-(As, Sb,andBi...
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