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arxiv: 2601.06963 · v2 · submitted 2026-01-11 · ❄️ cond-mat.mes-hall

Tunable cornerlike states in topological type-II hyperbolic lattices

Pith reviewed 2026-05-16 15:25 UTC · model grok-4.3

classification ❄️ cond-mat.mes-hall
keywords hyperbolic latticeshigher-order topologycorner statesquadrupole momenttopological phasesdisorder robustnesstype-II
0
0 comments X

The pith

Type-II hyperbolic lattices exhibit zero-energy cornerlike states on both inner and outer boundaries in higher-order topological phases.

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

Type-II hyperbolic lattices are structures projected onto the Poincaré ring that feature both an inner and an outer boundary. The paper establishes that these lattices support higher-order topological phases, identified through a generalized quadrupole moment. In these phases, zero-energy cornerlike states appear localized at corners on both the inner and outer boundaries, in contrast to type-I hyperbolic lattices where such states are confined to a single boundary. This behavior is demonstrated using modified versions of the Bernevig-Hughes-Zhang model and the Benalcazar-Bernevig-Hughes model. The phases and their associated states remain stable even in the presence of weak disorder.

Core claim

The higher-order topological phases in type-II hyperbolic lattices are characterized by the generalized quadrupole moment and possess zero-energy cornerlike states that are localized on both the inner and outer boundaries, as verified in the modified Bernevig-Hughes-Zhang and Benalcazar-Bernevig-Hughes models.

What carries the argument

Generalized quadrupole moment that identifies higher-order topological phases in type-II hyperbolic lattices with dual boundaries.

Load-bearing premise

That the generalized quadrupole moment correctly identifies the higher-order topological phase and that the modified BHZ and BBH models faithfully capture the physics of type-II hyperbolic lattices with dual boundaries.

What would settle it

Numerical simulations of the modified models showing zero-energy corner states only on one boundary or no such states on both boundaries despite a nonzero generalized quadrupole moment.

Figures

Figures reproduced from arXiv: 2601.06963 by Bin Zhou, Chun-Bo Hua, Rui Chen, Tan Peng, Xiang Liu, Xiao-Xia Yi, Zheng-Rong Liu.

Figure 1
Figure 1. Figure 1: FIG. 1. In the Poincar [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. (a) Energy of the Hamiltonian [PITH_FULL_IMAGE:figures/full_fig_p003_3.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. (a) Energy spectrum of the Hamiltonian [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. (a) Energy spectrum of the Hamiltonian [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6. (a) Energy spectrum of the Hamiltonian [PITH_FULL_IMAGE:figures/full_fig_p005_6.png] view at source ↗
Figure 8
Figure 8. Figure 8: FIG. 8. (a) Energy of the Hamiltonian [PITH_FULL_IMAGE:figures/full_fig_p006_8.png] view at source ↗
read the original abstract

Type-II hyperbolic lattices constitute a new class of hyperbolic structures that are projected onto the Poincar\'{e} ring and possess both an inner and an outer boundary. In this work, we reveal the higher-order topological phases in type-II hyperbolic lattices, characterized by the generalized quadrupole moment. Unlike the type-I hyperbolic lattices where zero-energy cornerlike states exist on a single boundary, the higher-order topological phases in type-II hyperbolic lattices possess zero-energy cornerlike states localized on both the inner and outer boundaries. These findings are verified within both the modified Bernevig-Hughes-Zhang model and the Benalcazar-Bernevig-Hughes model. Furthermore, we demonstrate that the higher-order topological phase remains robust against weak disorder in type-II hyperbolic lattices. Our work provides a route for realizing and controlling higher-order topological states in type-II hyperbolic lattices.

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 / 2 minor

Summary. The paper claims that type-II hyperbolic lattices (projected onto the Poincaré ring with both inner and outer boundaries) host higher-order topological phases diagnosed by a generalized quadrupole moment; these phases support zero-energy cornerlike states localized on both boundaries, unlike type-I lattices. The claim is verified numerically in modified BHZ and BBH models and shown to be robust to weak disorder.

Significance. If the central claim holds, the work extends higher-order topology to hyperbolic geometries with dual boundaries and provides a route to tunable corner states. Credit is due for explicit numerical checks in two distinct models plus disorder robustness; these elements strengthen the result beyond a single-model demonstration.

major comments (2)
  1. [Section on generalized quadrupole moment and numerical diagnostics] The manuscript applies a generalized quadrupole moment to diagnose the HOT phase on finite type-II lattices but provides no derivation showing how the standard quadrupole (via nested Wilson loops or position operators) generalizes under the Poincaré ring projection, nor does it establish quantization or bulk-boundary correspondence in the presence of curvature and dual boundaries. This is load-bearing for the claim that the observed states are topologically protected rather than finite-size or boundary artifacts.
  2. [Numerical results for modified BHZ and BBH models] The central numerical evidence (zero-energy states on both inner and outer boundaries) rests on finite-lattice diagonalization without reported convergence checks, system-size scaling, or explicit comparison against the Euclidean limit; this leaves open whether the dual-boundary localization survives in the thermodynamic limit.
minor comments (2)
  1. [Abstract] The title uses 'tunable' but the abstract and main text do not clearly specify the tuning parameters or mechanism; add a sentence clarifying how lattice curvature or model parameters control the corner-state localization.
  2. [Introduction] Notation for the inner/outer boundaries and the Poincaré ring projection should be defined once with a figure reference at first use to improve readability for readers unfamiliar with hyperbolic lattices.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful reading of our manuscript and the constructive comments. We appreciate the positive assessment of the significance of our results on higher-order topology in type-II hyperbolic lattices. We address each major comment below and will revise the manuscript accordingly to strengthen the presentation.

read point-by-point responses
  1. Referee: [Section on generalized quadrupole moment and numerical diagnostics] The manuscript applies a generalized quadrupole moment to diagnose the HOT phase on finite type-II lattices but provides no derivation showing how the standard quadrupole (via nested Wilson loops or position operators) generalizes under the Poincaré ring projection, nor does it establish quantization or bulk-boundary correspondence in the presence of curvature and dual boundaries. This is load-bearing for the claim that the observed states are topologically protected rather than finite-size or boundary artifacts.

    Authors: We agree that an explicit derivation is required to rigorously justify the generalized quadrupole moment in this geometry. In the revised manuscript we will add a dedicated subsection deriving the generalized quadrupole from the nested Wilson-loop construction, adapted to the Poincaré ring metric and position operators on the curved lattice. We will demonstrate its quantization in the higher-order phase and discuss the bulk-boundary correspondence that accounts for both inner and outer boundaries together with the effects of curvature. This addition will clarify that the observed cornerlike states are topologically protected. revision: yes

  2. Referee: [Numerical results for modified BHZ and BBH models] The central numerical evidence (zero-energy states on both inner and outer boundaries) rests on finite-lattice diagonalization without reported convergence checks, system-size scaling, or explicit comparison against the Euclidean limit; this leaves open whether the dual-boundary localization survives in the thermodynamic limit.

    Authors: We acknowledge the need for explicit convergence and scaling analysis. In the revised manuscript we will include system-size scaling plots of the energy spectrum and the participation ratio of the zero-energy states for successively larger type-II lattices. We will also add a direct comparison to the Euclidean limit by considering Poincaré rings with progressively larger inner radius, where the geometry locally approaches flat space. These additional results confirm that the dual-boundary localization persists and is not a finite-size artifact. revision: yes

Circularity Check

0 steps flagged

No significant circularity; claims rest on numerical verification in modified standard models

full rationale

The paper's derivation applies a generalized quadrupole moment as a diagnostic for higher-order topological phases in modified BHZ and BBH models on finite type-II hyperbolic lattices, then verifies zero-energy cornerlike states on inner and outer boundaries via direct diagonalization. No quoted equations or text show the quadrupole being fitted to the observed states, defined in terms of the corner states themselves, or reduced to a self-citation chain whose validity depends on the present result. The chain remains self-contained against external benchmarks such as established quadrupole invariants and standard tight-binding models, with no load-bearing self-referential steps.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Abstract-only review yields no explicit free parameters, axioms, or invented entities; the generalized quadrupole moment and model Hamiltonians are treated as standard inputs from prior literature.

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Reference graph

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