Equivalence class of Emergent Single Weyl fermion lattice models in 3 dimensions: gapless superconductors and superfluids versus chiral fermions
Pith reviewed 2026-05-18 02:56 UTC · model grok-4.3
The pith
Lattice models with single Weyl fermions in three dimensions all belong to one equivalence class in the infrared, isomorphic to topological superconductor critical points or their duals.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
In the infrared limit, all the lattice models with single Weyl fermions studied here are isomorphic to either a tQCP in a DIII class topological superconductor with a protecting T-symmetry, or its dual, a T-symmetry breaking superconducting nodal point phase, and therefore form an equivalent class. The proposal relies on spontaneous charge U(1) symmetry breaking to evade the usual no-go theorem of a single Weyl cone in a 3d lattice. For a generic T-symmetric tQCP the conserved-charge operators span a six-dimensional linear space while for a T-symmetry breaking gapless state charge operators typically span a two-dimensional linear space instead.
What carries the argument
Spontaneous breaking of U(1) charge symmetry applied to fermionic topological symmetry-protected states, which generates single Weyl cones or equivalent real-fermion nodal points whose infrared theories are isomorphic to DIII-class topological quantum critical points or their duals.
If this is right
- For generic T-symmetric tQCPs the conserved-charge operators span a six-dimensional linear space.
- For T-symmetry breaking gapless states the charge operators span a two-dimensional linear space.
- All the studied single-Weyl-fermion lattice models form one equivalence class in the infrared.
- Three-dimensional lattice chiral fermion models connect to gapless real fermions that appear in superfluids or superconductors.
Where Pith is reading between the lines
- Numerical simulations of the proposed models should reproduce identical low-energy spectra and correlation functions as the DIII tQCP or its dual.
- The charge-operator dimension difference offers a diagnostic to distinguish the T-symmetric and T-breaking members of the class.
- The constructions may extend to other symmetry classes or dimensions by applying analogous minimal topological changes or symmetry-breaking fields.
Load-bearing premise
The infrared effective theory after symmetry breaking contains precisely one Weyl cone or its real-fermion equivalent without extra gapless modes or instabilities.
What would settle it
A numerical diagonalization or renormalization-group analysis of one constructed lattice model that finds additional Weyl cones, extra gapless excitations, or instabilities differing from the expected DIII tQCP or nodal phase would disprove the isomorphism.
Figures
read the original abstract
In this article, we put forward a practical but generic approach towards constructing a large family of $(3+1)$ dimension lattice models which can naturally lead to a single Weyl cone in the infrared (IR) limit. Our proposal relies on spontaneous charge $U(1)$ symmetry breaking to evade the usual no-go theorem of a single Weyl cone in a 3d lattice. We have explored three concrete paths in this approach, all involving fermionic topological symmetry protected states (SPTs). Path a) is to push a gapped SPT in a 3d lattice with time-reversal symmetry (or $T$-symmetry) to a gapless topological quantum critical point (tQCP) which involves a minimum change of topologies,i.e. $\delta N_w=2$ where $\delta N_w$ is the change of winding numbers across the tQCP. Path b) is to peal off excessive degrees of freedom in the gapped SPT via applying $T$-symmetry breaking fields which naturally result in a pair of gapless nodal points of real fermions. Path c) is a hybrid of a) and b) where tQCPs, with $\delta N_w \geq 2$, are further subject to time-reversal-symmetry breaking actions. In the infrared limit, all the lattice models with single Weyl fermions studied here are isomorphic to either a tQCP in a DIII class topological superconductor with a protecting $T$-symmetry, or its dual, a $T$-symmetry breaking superconducting nodal point phase, and therefore form an equivalent class. For a generic $T$-symmetric tQCP along Path a), the conserved-charge operators span a six-dimensional linear space while for a $T$-symmetry breaking gapless state along Path b), c), charge operators typically span a two-dimensional linear space instead. Finally, we pinpoint connections between three spatial dimensional lattice chiral fermion models and gapless real fermions that can naturally appear in superfluids or superconductors studied previously.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes a generic approach to construct (3+1)D lattice models realizing a single Weyl cone in the IR limit via spontaneous charge U(1) symmetry breaking to evade no-go theorems. It outlines three paths from gapped 3d DIII-class SPTs: (a) driving to a tQCP with minimal topological change δN_w=2, (b) applying T-symmetry breaking fields to obtain a pair of gapless real-fermion nodal points, and (c) a hybrid of the two. The central claim is that all such models form an equivalence class isomorphic in the IR to either a T-symmetric tQCP in a DIII topological superconductor or its T-breaking dual (a superconducting nodal phase), with conserved-charge operators spanning a six-dimensional space in the former case and a two-dimensional space in the latter. Connections to gapless real fermions in superfluids and superconductors are noted.
Significance. If the constructions are shown to isolate precisely one Weyl cone (or real-fermion nodal pair) without extra gapless modes or instabilities, the work would provide a unifying framework for emergent single-Weyl lattice models, linking high-energy chiral fermions to condensed-matter gapless phases in topological superconductors and superfluids. The explicit distinction between six-dimensional and two-dimensional charge-operator spaces for T-symmetric versus T-breaking cases offers a concrete organizing principle. The approach of using minimal δN_w=2 changes and symmetry breaking to evade no-go theorems is a strength worth developing.
major comments (1)
- Abstract (central claim paragraph): The assertion that the models are isomorphic to a DIII tQCP or its T-breaking dual, with the IR containing precisely one Weyl cone without extra gapless modes, is load-bearing for the equivalence-class conclusion. This rests on the assumption that δN_w=2 plus the chosen symmetry-breaking fields (charge-U(1) breaking and T-breaking) isolate the target mode; however, no explicit lattice Hamiltonians, dispersion calculations, or full Brillouin-zone spectra are supplied to verify the absence of additional crossings or instabilities once the fields are applied.
minor comments (1)
- The abstract introduces δN_w without a brief definition or reference to the underlying topological invariant (e.g., winding number); a short clarification in the introduction would aid readability.
Simulated Author's Rebuttal
We thank the referee for their careful reading, positive assessment of the work's significance, and constructive feedback. We address the major comment below and will strengthen the manuscript with additional explicit details.
read point-by-point responses
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Referee: Abstract (central claim paragraph): The assertion that the models are isomorphic to a DIII tQCP or its T-breaking dual, with the IR containing precisely one Weyl cone without extra gapless modes, is load-bearing for the equivalence-class conclusion. This rests on the assumption that δN_w=2 plus the chosen symmetry-breaking fields (charge-U(1) breaking and T-breaking) isolate the target mode; however, no explicit lattice Hamiltonians, dispersion calculations, or full Brillouin-zone spectra are supplied to verify the absence of additional crossings or instabilities once the fields are applied.
Authors: We agree that the central claim would be strengthened by explicit verification. The manuscript develops a general construction based on minimal topological changes (δN_w=2) and controlled symmetry breaking to evade no-go theorems, with the equivalence class defined via IR effective theories and conserved charge operators (six-dimensional for T-symmetric tQCPs, two-dimensional for T-breaking cases). However, to directly address the concern, the revised manuscript will include concrete lattice Hamiltonians realizing each of the three paths, together with explicit low-energy dispersion relations and full Brillouin-zone spectra confirming that only the target single Weyl cone (or real-fermion nodal pair) remains gapless, with no additional crossings or instabilities introduced by the symmetry-breaking fields. These additions will make the isolation of the modes fully explicit while preserving the symmetry-based arguments. revision: yes
Circularity Check
Derivation chain is self-contained with no load-bearing reductions to inputs or self-citations
full rationale
The paper constructs explicit lattice models via three paths starting from gapped 3d SPTs in DIII class, driving them to tQCPs with δN_w=2 or applying T-breaking fields, then argues IR equivalence to known phases. No equations reduce the final isomorphism claim to a fitted parameter or prior self-citation by definition; the equivalence is presented as a consequence of the explicit constructions and symmetry analysis rather than a renaming or tautology. The isolation of single Weyl cones is an assumption about the spectrum after symmetry breaking, but this is an external physical claim, not a circular redefinition of the input models. The work is therefore self-contained against external benchmarks.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption Nielsen-Ninomiya no-go theorem prohibits a single Weyl cone on a lattice without symmetry breaking
- domain assumption Topological quantum critical points change winding number by δN_w = 2
Lean theorems connected to this paper
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IndisputableMonolith/Foundation/AlexanderDuality.leanalexander_duality_circle_linking echoes?
echoesECHOES: this paper passage has the same mathematical shape or conceptual pattern as the Recognition theorem, but is not a direct formal dependency.
We place ourselves in the 6-dimensional manifold T^3 × su(2)... Int(S, T^3 × {0}) ... sum of the signs of det(V) at every intersection point
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IndisputableMonolith/Foundation/RealityFromDistinction.leanreality_from_one_distinction unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
all the lattice models with single Weyl fermions ... isomorphic to either a tQCP in a DIII class topological superconductor ... or its dual
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.
Forward citations
Cited by 2 Pith papers
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Topologically shadowed quantum criticality: A non-compact conformal manifold
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Minimal-doubling and single-Weyl Hamiltonians
Minimal-doubling lattice fermion Hamiltonians yield single-Weyl phases when supplemented by a species-splitting mass term, but one-parameter symmetry-preserving deformations introduce additional Weyl nodes above a cri...
Reference graph
Works this paper leans on
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Patha) Following our discussion on real fermions, we will work with a general 4-band Hamiltonian in the real fermion representation: H= X k X i χT (k)A i(k)Γi χ(−k),Γ i = Γ† i ,Γ 2 i =I (22) whereΓ i are hermitian matrices. Contrary to Clifford algebras where only anticommut- ing matrices are involved, hereΓi andΓ j can either com- mute or anti-commute wi...
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[2]
a magnetic field along the z-direction)
Pathb) We start with the previous model in a gaped phase, ϵ̸= 0, and we add a T-breaking field (e.g. a magnetic field along the z-direction). We replaced3 +ϵbyµasϵ is no longer supposed to go to zero: 8 H(k) = sin(kx)Γ1 + sin(ky)Γ2 + sin(kz)Γ3 +M(k)Γ 4 +B(k)Γ 5 (30) where the massM(k)has been introduced in Eq.28. And following the algebras in Eq.27. one c...
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Weyl fermion in the real fermion formalism Let us first point out the real fermion expression of the Weyl fermion. In the standard complex formalism, a Weyl fermion with a given Handedness can be assigned with the following Hamiltonian Hcomplex(k) =k·σ(34) After transformation to real fermion formalism, a Weyl fermion is expressed as: 11 HReal(k) =k xσx +...
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[4]
The band structure in a strong magnetic field is shown in FIG
Projecting out the excessive degrees of freedom using the Schrieffer-Wolff transformation Now we begin with Hamiltonian (Eq.30) which can de- scribe a fully gapped SPT or in this case a DIII class topological superconductor subject to a magnetic field. The band structure in a strong magnetic field is shown in FIG. 4. The effect of a strong magnetic field ...
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belongs to one of Typecmodels in our classification withδN w = 8. We will focus of the UV completion of the emergent infrared single Weyl cone physics in gapless superfluids and corresponding conserved charge operators in lattice models in the momentum space of Torus-three,T3. Before starting detailed discussions, let us point out that the number of degre...
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This recent construction above is one example along Pathc), i.e
This quadruples the more generic tQCP fundamental value ofδN w = 2. This recent construction above is one example along Pathc), i.e. a hydrid approach of Path a) and Pathb). V) Finally, we also illustrate the differences in the con- struction of UV completed symmetries along different paths. For a genericT-symmetric tQCP along path a), the conserved-charg...
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discussion (0)
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