{"id":"8718ab8f-d2c8-412e-a50f-f07a2853f1bc","arxiv_id":"2508.19934","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":1,"one_line_summary":"Large planar Hall effect in EuAl2Si2 is dominated by classical orbital magnetoresistance in the ferromagnetic state and field-suppressed spin fluctuations above the ordering temperature, not by the chiral anomaly.","lead":"Researchers measured the planar Hall effect and anisotropic magnetoresistance in the antiferromagnet EuAl2Si2 across its field-driven magnetic transitions. The work shows the strong planar Hall signal comes mostly from classical orbital and spin-fluctuation mechanisms, not the topological chiral anomaly, giving a cautionary example for interpreting such signals.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Chiral-anomaly exclusion rests on a non-unique parametric plot and a missing quantitative comparison of PHE and AMR amplitudes; 'minor Berry-curvature role' is asserted, not quantitatively decomposed.","rationale":"The reader's verdict of CONDITIONAL is appropriate, and my concern supports it rather than changing it. The reader identified the symmetry protocol and fingerprint uniqueness as the weakest assumption. I agree that fingerprint uniqueness is load-bearing, but I locate the more concrete deficiency in the lack of a quantitative consistency check between the PHE amplitude and the AMR anisotropy. Because both mechanisms produce the same angular dependence, the B² scaling cannot discriminate; only the comparison of amplitudes (or a quantitative bound on n-MR) can. The parametric plot shape is not a reliable discriminator unless one models the field-dependence of ρ⊥ in both scenarios. The proposed test—comparing the fitted PHE amplitude to ρ⊥ − ρ//—would directly settle whether the transport is described by a single Δρ, which is the foundational assumption of Eqs. (4)–(5). If they match, the central claim survives but should be stated as an upper bound on the chiral anomaly contribution; if they do not, the claim fails. This does not move the verdict because the conditional rating already anticipates the need for such checks, but it sharpens the specific evidence required for acceptance.","tokens_in":9804,"tokens_out":11941,"duration_ms":140819,"concrete_test":"Re-analyze the symmetrized data at 2 K and 8 T: independently fit ρxyPHE(θ) to −A sinθcosθ and ρxxAMR(θ) to B − C cos²θ (using the raw, symmetrized data in Figs. 4b–c and 5a–b). Test whether A = C within experimental uncertainty. If A ≠ C, the single-Δρ model is invalid and an additional contribution (e.g., chiral anomaly or Berry curvature) is required. If A = C, then the PHE is exactly the angular projection of the AMR anisotropy, and the chiral-anomaly contribution is bounded by the experimental error on that equality; report this bound explicitly.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim that Berry curvature plays a minor role and that the PHE is dominated by classical orbital MR and spin-fluctuation suppression is not quantitatively substantiated. The paper shows that Δρ ∝ B², but the chiral anomaly also predicts Δρ ∝ B² (Eq. 6), as the authors themselves acknowledge. The distinguishing evidence is therefore the absence of negative longitudinal MR and the qualitative 'shock-wave' versus 'isotropic expansion' parametric plot shapes (Fig. 5c,f). However, the parametric plot shape is not a unique fingerprint: the standard AMR relation in Eq. (5) yields a circle in ρxy vs ρxx at fixed B, and the center of that circle shifts if ρ⊥ has a field dependence—exactly the situation in EuAl2Si2 where ρ⊥ grows strongly with B at 2 K. A chiral-anomaly contribution coexisting with a field-dependent ρ⊥ would produce the same shifted-circle 'shock-wave' appearance, so the observed pattern does not rule out a chiral-anomaly component. More fundamentally, Eq. (5) requires the same Δρ to appear in both the PHE amplitude and the AMR anisotropy. The paper never compares the independently fitted PHE amplitude with the measured ρ⊥ − ρ// at the same fields and temperatures. Without this comparison, the assertion that the PHE is fully accounted for by conventional mechanisms, with Berry curvature only minor, is not supported by any quantitative decomposition.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports planar Hall effect (PHE) and anisotropic magnetoresistance (AMR) measurements on the layered antiferromagnet EuAl2Si2 across the AFM–FM–PM phase boundaries. The authors purify the measured Hall and longitudinal signals using field and angle symmetrization (Eqs. 1–3) and find a PHE amplitude ~3.8 μΩ cm at 2 K and 8 T with sinθcosθ angular dependence and Δρ ∝ B². They argue that the PHE is not due to the chiral anomaly or Berry curvature but instead arises from classical orbital magnetoresistance in the field-induced FM state and field-suppressed spin fluctuations in the PM regime. The evidence includes the B² scaling, the absence of high-field negative longitudinal MR, the contrasting field dependence of ρ⊥ and ρ∥, and the qualitative shape of parametric ρxy–ρxx plots.","tokens_in":10124,"tokens_out":5255,"duration_ms":57414,"significance":"If the central claim is correct, the paper provides a useful counterexample to the common assignment of PHE in topological semimetals to the chiral anomaly, and it demonstrates that materials with tunable spin textures can host multiple coexisting conventional PHE mechanisms. The measurements are careful and the temperature/field phase coverage is broad. The paper also reports SdH oscillations and Berry-phase extraction, showing nontrivial topology in the FM state, which strengthens the platform. However, the quantitative mechanism decomposition is not fully substantiated: the key comparison between the PHE amplitude and the independently measured AMR anisotropy is missing, and the parametric ‘fingerprint’ argument is not unique. These issues are load-bearing for the main conclusion and require additional analysis.","major_comments":[{"comment":"Equation (5) assumes that the same parameter Δρ describes both the PHE amplitude and the AMR anisotropy: ρPHExy = -Δρ sinθcosθ and ρAMRxx = ρ⊥ - Δρ cos²θ. The authors fit Δρ from the PHE data (Figs. 4f,i) and separately show ρ⊥ and ρ∥ (Figs. 5b,e), but they never compare the fitted Δρ with the measured difference ρ⊥ - ρ∥ at the same temperatures and fields. Without this direct quantitative consistency check, the assertion that the PHE is fully accounted for by the AMR-related conventional mechanisms is not supported. A chiral-anomaly contribution added on top of the conventional AMR would obey the same angular forms and B² scaling; only by checking that the same Δρ quantitatively appears in both channels can conventional mechanisms be distinguished from a coexisting topological contribution.","section":"Section 2, Eq. (5) and Figs. 4f–i/5b,e"},{"comment":"The distinction between the ‘shock-wave’ pattern (FM state, 2 K) and ‘isotropic expansion’ pattern (PM state, 50 K) is presented as a unique mechanistic fingerprint. This is not justified. From Eq. (5), at fixed B the parametric plot of ρxy vs ρxx is a circle whose center shifts if ρ⊥ itself has a B-dependence. At 2 K, Fig. 5b shows that ρ⊥ grows strongly with B, so a shifted-circle/shock-wave appearance is exactly what would be expected from the conventional AMR relation—even if a chiral-anomaly term were also present. To make the fingerprint argument valid, the authors need to model the full field-dependent trajectory including ρ⊥(B), ρ∥(B), and a possible chiral term, and show that the observed shape excludes the latter quantitatively, rather than relying on qualitative pattern matching.","section":"Section 5, Fig. 5c,f"},{"comment":"The statement that “Berry curvature plays a minor role” is asserted but never quantitatively decomposed. The paper provides SdH Berry-phase measurements and Weyl-point locations (Figs. 3d,e), but these do not by themselves determine the Berry-curvature contribution to the PHE. No estimate—even a rough one—of the intrinsic Berry-curvature PHE is given, and no bound is placed on its magnitude relative to the observed 3.8 μΩ cm signal. As written, the conclusion is an interpretation consistent with the data, but it is not a demonstrated decomposition. This is a central claim of the abstract and should either be supported by a band-structure-based estimate or explicitly softened.","section":"Abstract and Conclusion"},{"comment":"The resistivity tensor written in Eq. (7) is not the standard inverse of the two-band conductivity tensor. For the transverse (B ⊥ current) configuration, the correct longitudinal resistivity is ρxx = σxx/(σxx² + σxy²), where σxx = σe/Δe + σh/Δh and σxy includes the Hall terms. Writing ρxx = (σe/Δe + σh/Δh)⁻¹ omits the σxy contribution and therefore cannot correctly produce the claimed high-field ρ⊥ ∝ B² scaling. The text also states that the model predicts B-independent ρxx, which is inconsistent with the second diagonal element in Eq. (7). Since this model is used to support the classical orbital origin of the B² scaling, the derivation needs to be corrected or the claim should be rephrased as qualitative rather than quantitative.","section":"Eq. (7), two-band model"}],"minor_comments":[{"comment":"Several typographical errors: “diffarction”, “chracterizations”, “microscop”, “finial”, “Soolids” (in Ref. 17), and “Le Common Met.” (in Ref. 14).","section":"Throughout"},{"comment":"The main text says MFM images were taken at 0.5 T, 3.8 T, and 4.7 T, while the caption of Fig. 2c–e lists 0 T, 3.8 T, and 4.7 T. Please clarify which field values are correct.","section":"Fig. 2 caption and text"},{"comment":"Refs. 3 and 27 are identical (Nandy et al., PRL 119, 176804). Please consolidate the duplicate reference.","section":"References"}],"recommendation":"major_revision","confidential_remarks":"The paper is well within the scope of the journal and addresses a timely topic. The main risk to the paper’s central claim is not the plausibility of conventional mechanisms but the lack of a quantitative consistency test between the PHE amplitude and the AMR anisotropy. If the authors can supply that comparison and correct the two-band model derivation, the paper would be substantially stronger. I would not recommend rejection, but the current version should not be accepted without these fixes."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Bottom line: this is a solid, careful experimental paper that makes a good case that the large planar Hall effect in EuAl2Si2 is conventional rather than a chiral anomaly signal. The central conclusion is probably right, but the quantitative decomposition promised in the abstract is not actually delivered.\n\nWhat's new: the PHE/AMR dataset for EuAl2Si2, including symmetrized angular sweeps from 2 K to 260 K and fields up to 9 T, plus the connection of the PHE to the field-driven AFM-FM transition. The measurement protocol in Eqs. (1)-(3) is sensible, and the authors are appropriately cautious that B² scaling and sinθcosθ angular dependence do not by themselves prove the chiral anomaly. The absence of negative longitudinal MR and the contrasting field dependence of ρ⊥ and ρ// are genuine evidence.\n\nThe soft spots are real but addressable. Most concretely, the paper never compares the fitted PHE amplitude with the independently measured AMR anisotropy ρ⊥−ρ// at the same fields and temperatures. Eq. (5) implies both should be controlled by the same Δρ, so a direct comparison would have been a decisive test. Instead we get a parametric plot whose 'shock-wave' pattern is presented as a unique fingerprint of orbital effects; it isn't, because a chiral anomaly contribution superimposed on a field-dependent ρ⊥ would produce the same shifted circle. The abstract's claim that Berry curvature plays a minor role has no quantitative support—no fitted Berry term, no upper bound, no comparison. There are no error bars and no raw data, which is unfortunate when the claim is a mechanism decomposition. The paper also acknowledges that the band topology for the in-plane polarized FM state was not calculated; the Weyl points come from c-axis polarization.\n\nNone of this sinks the paper. The evidence against a chiral-anomaly origin is solid, and the proposed conventional mechanisms are plausible. I would want to see the PHE/AMR comparison and some statement about how the Berry-curvature contribution was bounded before fully accepting the decomposition, but this deserves peer review. It's good material for a magnetotransport reading group.","headline":"Good experimental case against a chiral-anomaly origin for the PHE in EuAl2Si2, but the quantitative decomposition is asserted, not demonstrated.","tokens_in":10643,"tokens_out":4875,"would_cite":true,"duration_ms":54024,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"The planar Hall effect in EuAl2Si2 is shown to be conventional, not a chiral-anomaly signal: classical orbital magnetoresistance dominates the field-induced ferromagnetic state, and field-suppressed spin fluctuations dominate the paramagnet","keywords":["planar Hall effect","EuAl2Si2","topological antiferromagnet","Weyl semimetal","chiral anomaly","orbital magnetoresistance","spin fluctuations","anisotropic magnetoresistance"],"falsifier":"Fabricate a lithographically aligned Hall bar from the same EuAl2Si2 crystals and remeasure ρxyPHE under the same field and angle conditions. If the symmetrized ~3.8 μΩ cm amplitude and the shock-wave (2 K) and circular (50 K) parametric trajectories are reproduced, the reported effect is intrinsic; if the signal shrinks or the trajectories change shape, the dual-symmetrization protocol is generating part of the PHE from contact misalignment.","tokens_in":9718,"feed_emoji":"🧲","tokens_out":8312,"duration_ms":90345,"temperature":0.7,"pith_summary":"EuAl2Si2 is an antiferromagnet that a magnetic field drives into a ferromagnetic Weyl-semimetal state, so its planar Hall effect (PHE) is a natural place to look for the chiral anomaly. The paper argues that the measured PHE—about 3.8 μΩ cm at 2 K and 8 T—is real but not topological. After symmetrizing raw signals to remove ordinary Hall and contact-misalignment admixtures, the authors find the expected sinθcosθ angular form, yet the amplitude grows as B², no negative longitudinal magnetoresistance appears, and the parametric ρxy–ρxx traces have 'shock-wave' or circular shapes. They attribute the effect to two conventional mechanisms: classical orbital magnetoresistance in the field-induced ferromagnetic state, and field suppression of spin-fluctuation scattering above the Néel temperature. If correct, chiral-anomaly interpretation is not needed here, and the same fingerprints can mislead in other topological magnets.","feed_headline":"Planar Hall effect in EuAl2Si2 is classical, not topological","feed_subtitle":"Symmetry-cleaned data at 2–260 K show orbital magnetoresistance and spin fluctuations mimic the chiral-anomaly fingerprint.","key_machinery":"The load-bearing object is the dual-symmetrization protocol: field averaging ρxy(+B,θ) and ρxy(−B,θ) removes the ordinary Hall component, and antisymmetrization between θ and π−θ removes AMR leakage from contact misalignment, with analogous purification of ρxx. This isolates an intrinsic planar Hall resistivity whose sinθcosθ form, B² field scaling, and parametric ρxy-versus-ρxx trajectories are compared against two competing models: chiral-anomaly theory (Δρ ∝ (Lc/La)², isotropic parametric expansion) and a classical two-band orbital model (ρ⊥ ∝ μeμhB², producing the 'shock-wave' asymmetry). The contrasting circular trajectory above TN identifies the spin-fluctuation contribution.","core_discovery":"EuAl2Si2 is an A-type antiferromagnet (TN ≈ 33.6 K) that a magnetic field drives into a ferromagnetic Weyl-semimetal state, so its planar Hall effect (PHE) is a natural chiral-anomaly candidate. The paper's central claim is that the measured PHE, ≈3.8 μΩ cm at 2 K and 8 T, is not topological. After dual symmetrization removes ordinary-Hall and misalignment admixtures, the signal keeps its sinθcosθ form and B² scaling, but no negative longitudinal magnetoresistance appears in the ferromagnetic phase, and the parametric ρxy–ρxx plots form 'shock-wave' (2 K) and circular (50 K) trajectories. The paper attributes these to classical two-band orbital magnetoresistance (FM state) and field-suppress","pith_inferences":["A natural check the paper leaves implicit: measure the same PHE in electron-beam-lithographed Hall bars with perfectly aligned contacts; if the symmetrized amplitude drops or the shock-wave shape changes, part of the reported signal is a contact artifact rather than intrinsic transport.","The paper's parametric classification suggests a broader diagnostic: for any claimed chiral-anomaly PHE, the ρxy–ρxx plot should be nearly isotropic; anisotropic 'shock-wave' trajectories indicate an orbital origin instead.","Because the Weyl points were calculated only for the c-axis-polarized ferromagnetic state, the in-plane-polarized FM topology remains unexplored; repeating the SdH and PHE analysis with B along intermediate in-plane directions could reveal whether the orbital PHE amplitude tracks the Weyl-band geometry.","If spin-fluctuation suppression drives the paramagnetic PHE, its amplitude above TN should correlate quantitatively with the field-induced magnetization or susceptibility change; comparing Δρ(T,B) with M(T,B) would give a direct test."],"forward_implications":["A B²-scaling, sinθcosθ planar Hall signal is not by itself evidence of a chiral anomaly; the same fingerprints arise from classical orbital magnetoresistance and spin-fluctuation scattering in a magnetic multiband metal.","The dual-symmetrization protocol can be applied to other topological magnets to separate genuine topological PHE from misalignment and ordinary-Hall contamination before claiming chiral anomaly.","In the field-induced ferromagnetic state, the PHE amplitude is controlled by carrier mobilities and can in principle be tuned by doping or by shifting the Weyl points relative to the Fermi level.","Above the Néel temperature, the PHE tracks the suppression of thermal spin fluctuations, giving a transport-based window onto magnetic scattering in the paramagnetic phase.","Because the same crystal passes through AFM, FM, and PM states, temperature- and field-dependent PHE maps the phase diagram and the spin-texture reconfigurations that accompany it."],"supporting_citations":[{"why":"Prior report of EuAl2Si2 as an AFM axion insulator with a field-induced FM Weyl state, supplying crystals, high-field MR, band structure, and MFM domain evolution.","marker":"[8]"},{"why":"Theory that chiral anomaly produces sinθcosθ planar Hall and Δρ ∝ (Lc/La)²; the predicted signature the paper tests.","marker":"[27]"},{"why":"Experimental tests in Na3Bi and GdPtBi showing classical orbital magnetoresistance can mimic chiral-anomaly signals.","marker":"[26]"},{"why":"Chiral-anomaly transport study of GdPtBi used as the isotropic parametric benchmark.","marker":"[32]"},{"why":"Evidence for the chiral anomaly in Na3Bi whose parametric behavior the FM 'shock-wave' pattern is contrasted with.","marker":"[33]"},{"why":"Protocol for removing probe-misalignment admixture of AMR from the planar Hall signal.","marker":"[7]"},{"why":"Theoretical origin of the planar Hall effect in Weyl semimetals from chiral anomaly, the hypothesis the paper argues against.","marker":"[3]"},{"why":"Nontopological origin of the planar Hall effect in NiTe2, supporting that orbital mechanisms can reproduce chiral-anomaly-like PHE.","marker":"[31]"}],"fun_headline_variants":["EuAl2Si2 planar Hall effect: classical, not chiral anomaly","Classical orbital MR drives planar Hall effect in EuAl2Si2","Planar Hall effect in EuAl2Si2 traced to classical origins","No chiral anomaly: EuAl2Si2 planar Hall effect is classical"],"cache_read_input_tokens":2688,"weakest_assumption_plain":"The result stands on the assumption that Eqs. (1)–(3) completely remove ordinary-Hall and contact-misalignment admixtures, leaving an intrinsic PHE, and that the ρxy-versus-ρxx plot shape uniquely distinguishes orbital and spin-fluctuation mechanisms from the chiral anomaly.","fun_headline_variants_meta":{"raw":{"variants":["EuAl2Si2 planar Hall effect: classical, not chiral anomaly","Classical orbital MR drives planar Hall effect in EuAl2Si2","Planar Hall effect in EuAl2Si2 traced to classical origins","No chiral anomaly: EuAl2Si2 planar Hall effect is classical"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001343,"raw_usage":{"total_tokens":5312,"prompt_tokens":780,"completion_tokens":4532,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":524,"completion_tokens_details":{"reasoning_tokens":4453}},"tokens_in":524,"tokens_out":4532,"duration_ms":28899,"temperature":1.0,"reasoning_tokens":4453,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-05T15:20:20.780281+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Fabricate a lithographically aligned Hall bar from the same EuAl2Si2 crystals and remeasure ρxyPHE under the same field and angle conditions. If the symmetrized ~3.8 μΩ cm amplitude and the shock-wave (2 K) and circular (50 K) parametric trajectories are reproduced, the reported effect is intrinsic; if the signal shrinks or the trajectories change shape, the dual-symmetrization protocol is generating part of the PHE from contact misalignment.","supporting_citations":[{"cited_title":"Giant domain wall anomalous Hall effect in a layered antiferromagnet EuAl2Si2,","cited_arxiv_id":null,"evidence_quote":"Prior report of EuAl2Si2 as an AFM axion insulator with a field-induced FM Weyl state, supplying crystals, high-field MR, band structure, and MFM domain evolution."},{"cited_title":"Chiral anomaly as the origin of the planar Hall effect in Weyl semimetals,","cited_arxiv_id":null,"evidence_quote":"Theory that chiral anomaly produces sinθcosθ planar Hall and Δρ ∝ (Lc/La)²; the predicted signature the paper tests."},{"cited_title":"Experimental tests of the chiral anomaly magnetoresistance in the Dirac-Weyl semimetals Na3Bi and GdPtBi,","cited_arxiv_id":null,"evidence_quote":"Experimental tests in Na3Bi and GdPtBi showing classical orbital magnetoresistance can mimic chiral-anomaly signals."},{"cited_title":"The chiral anomaly and thermopower of Weyl fermions in the half-Heusler GdPtBi,","cited_arxiv_id":null,"evidence_quote":"Chiral-anomaly transport study of GdPtBi used as the isotropic parametric benchmark."},{"cited_title":"Evidence for the chiral anomaly in the Dirac semimetal Na 3Bi,","cited_arxiv_id":null,"evidence_quote":"Evidence for the chiral anomaly in Na3Bi whose parametric behavior the FM 'shock-wave' pattern is contrasted with."},{"cited_title":"Planar Hall effect in the quasi -one-dimensional topological superconductor TaSe3,","cited_arxiv_id":null,"evidence_quote":"Protocol for removing probe-misalignment admixture of AMR from the planar Hall signal."},{"cited_title":"Nontopological origin of the planar Hall effect in the type -II Dirac semimetal NiTe2,","cited_arxiv_id":null,"evidence_quote":"Nontopological origin of the planar Hall effect in NiTe2, supporting that orbital mechanisms can reproduce chiral-anomaly-like PHE."}],"review_version":1}