{"id":"14af2810-6ca7-4b6d-9b4d-6cd65ca5b289","arxiv_id":"2607.25688","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"Antichiral hinge states, one-dimensional edge channels that propagate in the same direction on opposite sides, are experimentally observed in a higher-order photonic nodal ring semimetal and can be repositioned by layer stacking.","lead":"This paper reports the first observation of antichiral hinge states: one-dimensional boundary modes on two opposite edges that carry microwaves in the same direction, realized in a three-dimensional gyromagnetic photonic crystal. A generalist should read it because it completes a missing class of topological boundary transport and shows reconfigurable, backscattering-immune photonic routing.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Predicted A–C hinge selection is not independently established: the termination-dependent unit-cell convention and Eq. (2) are invoked after the hinge positions are observed, so a direct open-boundary eigenmode calculation is needed.","rationale":"Reader's conditional verdict is appropriate. The measured co-propagating hinge modes, their 30 dB forward/backward asymmetry, robustness to metal obstacles, and the layer-dependent reconfiguration are strong experimental evidence for the existence of the states, and I see no internal inconsistency in the data. The concern I share is narrower: the theoretical selection of the two specific hinges rests on Eq. (2) evaluated with a termination-dependent unit-cell convention that is introduced after the observed pattern is known, and Eq. (2) is conceded to hold only where the surface band is isolated. This does not falsify the observation, but it weakens the claim that the hierarchy is derived rather than interpreted. A direct finite-sample eigenmode calculation with actual open boundaries would remove the gauge ambiguity and is a normal computational check. Secondary points (no deposited code, no error-bar statistics, no explicit trivial control) reinforce the conditional verdict but are not necessary to the main objection. I therefore leave the reader's CONDITIONAL verdict unchanged.","tokens_in":11190,"tokens_out":8739,"duration_ms":78366,"concrete_test":"Use the published tight-binding model (or COMSOL geometry) with open/PEC boundaries along both y and z for the 11-layer sample, with no use of Eq. (2) or any chosen unit-cell origin, and enumerate all eigenmodes in 7.0–8.8 GHz, recording the spatial support on hinges A–D. The concern is settled if the only localized modes are on A and C; if B or D also carry modes, or if shifting the unit-cell origin by one layer changes the predicted pattern, the diagonal-selection rule is not physical. Repeat for the 12-layer (one added layer) case to test the A/B prediction.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim is the first observation of antichiral hinge states, and the decisive interpretive step is the rule that selects hinges A and C (and later A and B). The text states: 'For the odd-layer sample, the two-layer unit cells defined from the top and bottom boundaries differ by one layer; therefore, the surface polarization for the same lateral surface has 1/2 at one z-termination but 0 at the other.' This sentence appears only after the A–C pattern has been reported, and the same paragraph concedes that Eq. (2) 'is valid only in the wavevector region where the antichiral surface band remains isolated from the projected bulk continuum.' A unit-cell origin is a gauge choice; if the physical termination does not uniquely fix the convention before comparing with data, the surface-polarization mismatch can be arranged to match whichever hinges show modes. The paper does not present a full open-boundary eigenmode computation showing that A and C are the unique hinge-localized channels for the actual 11-layer termination, nor a blind calculation for the 12-layer reconfiguration. Without that, the higher-order hierarchy interpretation is a plausible explanation rather than an independently derived prediction.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports the theoretical proposal and experimental observation of antichiral hinge states in a three-dimensional gyromagnetic photonic crystal that realizes a higher-order nodal-ring semimetal. The authors design a periodic stack of modified Haldane layers with alternating interlayer couplings, producing bulk nodal rings and Dirac lines. Near-field scanning measurements reveal drumhead surface states, antichiral surface states with positive group velocity, and a pair of hinge states at two parallel hinges propagating unidirectionally in the same direction, with claimed robustness against metallic scatterers. Adding or removing a photonic layer is shown to reconfigure the spatial locations of the hinge states. The interpretation uses surface-polarization and termination-dependent unit-cell arguments to identify the observed diagonal hinge selection as a higher-order topological response.","tokens_in":11423,"tokens_out":6241,"duration_ms":54701,"significance":"If the central claim holds, this is the first experimental realization of antichiral hinge states in a higher-order topological semimetal, extending antichiral boundary transport beyond first-order systems and demonstrating a hierarchy of drumhead, antichiral surface, and hinge states in one platform. The evidence is multi-pronged: near-field field maps at multiple hinges, transmission spectra with up to about 30 dB forward/backward contrast, measured dispersions with positive group velocity, and a layer-addition reconfiguration experiment. The manuscript also explicitly states the validity regime of the surface-polarization criterion, which is a useful limitation. However, the load-bearing interpretive step—the selection of specific hinges—depends on a termination-dependent unit-cell convention that is introduced after the observation, and the robustness claim lacks quantitative backscattering data. These gaps are fixable and do not negate the experimental observation, but they must be addressed to make the higher-order hierarchy interpretation convincing.","major_comments":[{"comment":"The selection of hinges A and C is presented as a prediction of the surface-polarization criterion after those hinges were observed. The unit-cell convention for the odd-layer sample is introduced in this paragraph, and Eq. (2) is acknowledged to be valid only where the antichiral surface band is isolated from the projected bulk continuum. Because surface polarization is a bulk quantity that depends on the unit-cell choice, the physical termination must uniquely determine the convention used for the top and bottom boundaries. The manuscript does not show that the actual 11-layer copper-plate termination forces the 1/2-versus-0 assignment, nor does it report an open-boundary eigenmode calculation (with PEC boundaries along y and z, as described in Methods) that resolves the hinge positions to A and C from the real-space termination alone. Please provide this direct eigenmode calculation or a detailed termination-resolved surface-polarization derivation, and likewise for the 12-layer sample, so that the hinge selection is an independently derived consequence of the model rather than a post hoc assignment.","section":"Experimental observation of antichiral hinge states, paragraph starting 'Notably, both diagonal hinges...' and…"},{"comment":"Robustness to metallic scatterers is asserted qualitatively from near-field maps showing no obvious increase in reflected-field intensity. The abstract claims 'robust transport against metallic scatterers', but no quantitative transmission measurements with and without obstacles are provided. Please report forward and backward transmission spectra (or S-parameters) for the pristine and obstructed hinges, including repeated measurements or uncertainty estimates, to substantiate the backscattering-immune behavior in the presence of defects.","section":"Experimental observation of antichiral hinge states, Fig. 3d–g"},{"comment":"The reconfiguration from hinges A/C to hinges A/B is explained by a change in surface polarization induced by the added Dirac semimetal layer, but no computed surface polarization for the 12-layer termination or an eigenmode calculation of the reconfigured hinge states is shown. This is the same termination-dependence issue as in the odd-layer case. The reader should be able to verify that the same criterion applied to the 12-layer sample yields hinges A and B; without that, the 'on-demand control' claim rests on a single experimental observation without independent theoretical support.","section":"Spatial reconfiguration of the antichiral hinge states, Fig. 4"}],"minor_comments":[{"comment":"There are spacing/OCR artifacts in several early uses of key terms (e.g., 'a ntichiral hinge state s', 'high er-order', 'e dge states' in the first paragraph). These should be cleaned in the final typeset version.","section":"Abstract and Introduction"},{"comment":"The 'up to approximately 30 dB' forward/backward contrast is quoted without specifying the frequency range over which the contrast is large. Please state the frequency band where the contrast exceeds, say, 20 dB, and indicate whether the contrast degrades near the nodal-ring frequencies.","section":"Fig. 3b"},{"comment":"The statement that Eq. (2) is valid only where the antichiral surface band is isolated from the projected bulk continuum should be reconciled with the measured hinge-state dispersion, which must be defined over an actual frequency band. Clarify how the hinge state is identified in the wavevector regions where the surface polarization is ill-defined.","section":"Experimental observation of antichiral hinge states, paragraph after Eq. (2)"},{"comment":"The codes are available only 'upon request'. For reproducibility, consider depositing the tight-binding model and the COMSOL simulation scripts in a permanent public repository.","section":"Code availability"}],"recommendation":"major_revision","confidential_remarks":"The referee agrees with the stress-test concern: the termination-dependent unit-cell convention is the weakest link in the theoretical interpretation of the hinge selection. If the authors already possess the open-boundary eigenmode data that resolve the hinge positions, adding it would be a straightforward and decisive fix; if not, the claim of an intrinsically predicted higher-order hierarchy will remain under-supported. The experimental observation itself appears credible and important, but the current manuscript should not be accepted without this verification and the quantitative robustness data."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Dear Colleague,\n\nThe headline: this is a credible first observation of antichiral hinge states, supported by multiple measurements, but the theoretical rule that picks out hinges A and C is introduced after the fact and needs an independent check.\n\nWhat is actually new: the paper reports the first experimental realization of antichiral hinge states, the higher-order counterpart of previously observed antichiral edge/surface states. The sample is a 3D gyromagnetic photonic crystal hosting nodal rings and Dirac lines. The key observation is two parallel one-dimensional hinges (A and C) with copropagating unidirectional transport, confirmed by near-field maps, transmission spectra with up to roughly 30 dB forward/backward contrast, positive-group-velocity dispersions, and robustness to metallic obstacles. The hinge positions shift when a layer is added, which is a nice demonstration of reconfigurability. The paper also shows drumhead and antichiral surface states in the same platform, making the case for a full hierarchy. That is a solid advance for topological photonics.\n\nThe soft spots are moderate. The central observation of copropagating hinge modes is well supported. The weaker link is the explanation of why hinges A and C are chosen. The paper invokes a termination-dependent unit-cell convention and the surface polarization of Eq. (2) after having observed the diagonal pattern. That looks partly post hoc. A direct open-boundary eigenmode calculation for the actual 11-layer and 12-layer terminations would settle whether the theory independently predicts the diagonal selection. The paper reports some calculated hinge dispersions, but the selection rule itself is not clearly derived from first principles. This matters for the claim of a higher-order hierarchy, though not for the basic fact that antichiral hinge transport exists. Minor quibbles: no error bars or repeat statistics on the transmission data, and the 'reconfiguration' is manual layer addition rather than dynamic control. Neither is disqualifying for a proof-of-concept experiment.\n\nThe citation pattern is fine; the prior proposals and related observations are cited. The model is purpose-built, but that is normal for this kind of design.\n\nWho this is for: anyone in topological photonics, especially people working on higher-order topological semimetals or nonreciprocal routing. It deserves a serious referee. The experiment appears to be the first of its kind and the core data are convincing. I would send it to review, with a request that the referee ask for an open-boundary eigenmode calculation making the hinge-selection prediction explicit, and ideally some repeated transmission measurements.\n\nBest","headline":"A credible first observation of antichiral hinge states in a photonic crystal, though the hinge-selection rule would benefit from a direct open-boundary eigenmode calculation.","tokens_in":12019,"tokens_out":2968,"would_cite":true,"duration_ms":25522,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"A pair of antichiral hinge states is observed in a 3D photonic nodal-ring semimetal, with both hinges carrying unidirectional modes in the same direction.","keywords":["antichiral hinge states","higher-order topological semimetal","nodal ring semimetal","gyromagnetic photonic crystal","surface polarization","drumhead surface states","topological photonics","unidirectional transport"],"falsifier":"Recompute the surface polarization of the antichiral surface band with the termination-defining unit cell shifted by one layer: the criterion then predicts the opposite diagonal hinge pair. Measuring which pair actually carries unidirectional modes in a sample with that termination would settle whether the hierarchy is determined by surface polarization.","tokens_in":10987,"feed_emoji":"🧭","tokens_out":4497,"duration_ms":37837,"temperature":0.7,"pith_summary":"The paper reports the experimental observation of antichiral hinge states—one-dimensional boundary modes that propagate in the same direction on two parallel hinges even though the system is closed. Working with a three-dimensional gyromagnetic photonic crystal whose bulk is a nodal-ring semimetal, the authors show that two diagonal hinges each carry a unidirectional mode of the same chirality, with the expected counter-propagating channels replaced by gapless bulk modes. They also observe drumhead surface states and antichiral surface states in the same sample, forming a full hierarchy of first- and second-order topological boundary states. If correct, this is the first realization of antichiral transport in a higher-order topological semimetal, and it demonstrates a reconfigurable on-chip routing platform.","feed_headline":"Antichiral hinge states carry light one way along two hinges","feed_subtitle":"A 3D photonic crystal with nodal rings hosts hinge modes that share a direction and can be repositioned by one layer.","key_machinery":"The central object is the termination-dependent surface polarization $\\nu_z^{\\mathrm{surface}}(k_x)$, computed as the Berry phase of the isolated antichiral surface band along $k_z$. A value of $1/2$ in the momentum window $2/3 < k_x/(\\pi/a) < 4/3$ predicts a hinge state wherever this polarization changes from $1/2$ to $0$ between two boundaries. The antichiral surface band itself provides the two-dimensional topological channel, so the one-dimensional hinge response is governed by the topology of that surface band, in analogy to an SSH chain of coupled surface layers.","core_discovery":"In a designed 3D photonic crystal made of stacked gyromagnetic layers with alternating interlayer couplings, the bulk hosts two nodal rings at shifted frequencies plus vertical Dirac lines. Near-field microwave measurements show that two parallel diagonal hinges—and only those—carry co-propagating unidirectional modes in the 7.0–8.8 GHz window between the rings, with transmission contrast up to about 30 dB and no backscattering from metallic obstacles. The hinge positions are set by a surface polarization of 1/2 that lives on the antichiral surface band, and adding a single photonic layer moves the hinge from one diagonal pair to the other. The authors interpret the hinge states as the higher-order counterpart of previously observed antichiral edge and surface states.","pith_inferences":["If the surface-polarization mechanism is robust, the same stacking principle could be translated to other wave domains where gyromagnetic response is unavailable, using time-reversal-breaking analogues in acoustics or mechanics.","The co-propagating hinge modes cannot close a loop on a rectangular block, but a triangular-prism geometry would allow such loops; one could test whether this enables a three-dimensional one-way circulator.","Dynamic control of the interlayer coupling, for instance by mechanically tuning layer spacing or using shutters at the coupling holes, might extend the demonstrated static reconfiguration into fast switching of hinge channels.","The surface-polarization criterion is valid only where the antichiral surface band is isolated from the bulk continuum; a testable extension is whether coupling the surface states into the bulk continuum softens or removes the protection over wider frequency bands."],"forward_implications":["Antichiral transport now extends into higher-order topology: the previously missing class of unidirectional boundary channels in three dimensions is filled, so gapless higher-order semimetals become a general setting for one-way hinge transport.","Hinge channels are reconfigurable by adding or removing a photonic layer, allowing on-demand selection of which edges route light without refabrication.","The observed robustness against metallic scatterers, with no obvious increase in reflected field intensity, supports the use of these channels as reconfigurable nonreciprocal waveguides.","The coexistence of drumhead surface states, antichiral surface states, and hinge states in one sample demonstrates that a single semimetal can host a complete hierarchy of topological boundary responses."],"supporting_citations":[{"why":"Introduces the concept of antichiral edge states in a modified Haldane model, the first-order effect this work lifts to hinges.","marker":"[12]"},{"why":"Reports the first photonic antichiral edge states, providing the experimental platform concept that the stacked layers build on.","marker":"[13]"},{"why":"Reports antichiral surface states in a magnetic Weyl photonic crystal, the direct three-dimensional predecessor for the surface bands used here.","marker":"[16]"},{"why":"Demonstrates chiral hinge states in a photonic axion insulator, the higher-order chiral counterpart whose antichiral version was missing.","marker":"[17]"},{"why":"Provides a theoretical proposal of antichiral hinge states based on coupled Haldane models, which this work realizes in a real-space photonic crystal.","marker":"[22]"},{"why":"Proposes tunable antichiral hinge states in photonic synthetic dimensions, an alternative route that this work replaces with an intrinsic 3D structure.","marker":"[23]"},{"why":"Defines the bulk polarization and multipole formalism used to derive the surface-polarization criterion.","marker":"[33]"},{"why":"Supplies the SSH-model analogy used to explain hinge formation as a polarization effect of the surface band.","marker":"[35]"}],"fun_headline_variants":["Antichiral hinge states share one direction on two hinges","Higher-order antichiral hinge states appear in photonic crystal","Same-direction hinge modes defy chirality cancellation","Co-propagating hinge states appear in a nodal-ring semimetal","Reconfigurable antichiral hinges offer robust photonic routing"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The argument's load-bearing premise is that a chosen convention for grouping layers into unit cells, anchored at the top versus bottom boundary, is not merely a bookkeeping choice but is physically forced; if that convention is arbitrary, the predicted diagonal hinge positions do not follow from the theory alone.","fun_headline_variants_meta":{"raw":{"variants":["Antichiral hinge states share one direction on two hinges","Higher-order antichiral hinge states appear in photonic crystal","Same-direction hinge modes defy chirality cancellation","Co-propagating hinge states appear in a nodal-ring semimetal","Reconfigurable antichiral hinges offer robust photonic routing"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.00112,"raw_usage":{"total_tokens":4630,"prompt_tokens":883,"completion_tokens":3747,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":499,"completion_tokens_details":{"reasoning_tokens":3664}},"tokens_in":499,"tokens_out":3747,"duration_ms":24221,"temperature":1.0,"reasoning_tokens":3664,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T15:25:21.567665+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Recompute the surface polarization of the antichiral surface band with the termination-defining unit cell shifted by one layer: the criterion then predicts the opposite diagonal hinge pair. Measuring which pair actually carries unidirectional modes in a sample with that termination would settle whether the hierarchy is determined by surface polarization.","supporting_citations":[{"cited_title":"& Franz, M","cited_arxiv_id":null,"evidence_quote":"Introduces the concept of antichiral edge states in a modified Haldane model, the first-order effect this work lifts to hinges."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Reports the first photonic antichiral edge states, providing the experimental platform concept that the stacked layers build on."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Reports antichiral surface states in a magnetic Weyl photonic crystal, the direct three-dimensional predecessor for the surface bands used here."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Demonstrates chiral hinge states in a photonic axion insulator, the higher-order chiral counterpart whose antichiral version was missing."},{"cited_title":"& Jia, S","cited_arxiv_id":null,"evidence_quote":"Provides a theoretical proposal of antichiral hinge states based on coupled Haldane models, which this work realizes in a real-space photonic crystal."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Proposes tunable antichiral hinge states in photonic synthetic dimensions, an alternative route that this work replaces with an intrinsic 3D structure."},{"cited_title":"A., Bernevig, B","cited_arxiv_id":null,"evidence_quote":"Defines the bulk polarization and multipole formalism used to derive the surface-polarization criterion."},{"cited_title":"P., Schrieffer, J","cited_arxiv_id":null,"evidence_quote":"Supplies the SSH-model analogy used to explain hinge formation as a polarization effect of the surface band."}],"review_version":1}