{"id":"43318c74-f623-4119-a915-392c5a9866fb","arxiv_id":"2411.11395","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":7.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":1,"one_line_summary":"TbMn6Sn6 shows strong, field-tunable second-harmonic transport at room temperature, attributed to the quantum metric dipole and Berry curvature dipole.","lead":"This paper reports a large, magnetic-field-tunable second-harmonic voltage in the kagome magnet TbMn6Sn6 at room temperature, near its spin-reorientation transition. The authors interpret the signal as a mix of quantum metric, Berry curvature and skyrmion contributions, a combination that could matter for nonlinear electronic devices working without cryogenics.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The quantum metric attribution hinges on a static in-plane antiferromagnetic Mn canting that is not established: the cited INS 'flat-band antiferromagnetism' is a spin-wave feature, and the 13° tilt is a coherent ferromagnetic canted component. Without static P-breaking, Dmetric=0.","rationale":"The paper's empirical observation of a large, field-tunable second-harmonic transport response near 300 K is plausible, and the transport data appear carefully collected; the Sample 1 versus Sample 2 comparison and the scaling analysis in Fig. S11 address some extrinsic contributions. Credit is also due for benchmarking against known materials in Fig. 3C. However, the central novelty is the quantum metric interpretation, and that interpretation requires inversion breaking in the electronic band structure. In a centrosymmetric kagome ferrimagnet, the only proposed source of P-breaking is a static 'flat-band antiferromagnetic' in-plane arrangement of Mn moments. The references to inelastic neutron scattering do not prove this arrangement is static: 'flat-band antiferromagnetism' in ref. 17 is a classification of spin-wave excitations in ferromagnetic kagome layers, and the ~13° canting from ref. 29 is a coherent moment tilt whose in-plane projection is ferromagnetic and therefore P-even. Without static magnetic Bragg evidence for the AFM sublattice, Dmetric has no microscopic support. This concern is more specific than a generic 'missing computation': even a perfect Dmetric calculation using the proposed texture would be irrelevant if the texture is not the equilibrium state. The neutron diffraction test proposed above settles the question. The reader's weakest assumption identified the same hidden in-plane AFM texture, so I agree with that read, and the verdict remains CONDITIONAL/UNCHANGED pending that evidence.","tokens_in":9873,"tokens_out":6678,"duration_ms":75972,"concrete_test":"Perform polarized single-crystal neutron diffraction (or resonant elastic X-ray scattering) at 300 K on the same TbMn6Sn6 crystals, searching for magnetic superlattice reflections with the propagation vector and spin polarization expected for the claimed flat-band antiferromagnetic in-plane canting. Compare elastic (E≈0) intensity with the inelastic spin-wave intensity reported in ref. 17. If no static magnetic Bragg peak is observed and the flat-band feature is purely inelastic, the P-breaking condition for Dmetric is absent, and ΔV2ω must be re-analyzed without a quantum metric contribution. As a complementary check, compute Dmetric from DFT/Wannier bands using the accepted collinear c-axis ferrimagnetic structure; if it vanishes, the quantum metric attribution is refuted.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's central attribution of the odd-in-field second-harmonic voltage to a quantum metric dipole rests on one premise: that the Mn kagome planes host a static, inversion-breaking in-plane antiferromagnetic texture at room temperature. The evidence cited is (i) a ~13° canting angle from ref. 29 and (ii) inelastic neutron scattering features classified as 'flat-band antiferromagnetism' and 'chiral antiferromagnetism' from ref. 17. Neither establishes a static P-breaking texture. The 13° canting is a coherent tilt of the ferrimagnetic moments, whose in-plane projection is ferromagnetic, not antiferromagnetic; a uniform in-plane ferromagnetic component does not break inversion symmetry. The INS 'flat-band antiferromagnetism' is a spin-wave excitation branch on the ferromagnetic kagome lattice, not a magnetic Bragg peak; it demonstrates a dynamic correlation, not a static spin arrangement. If no static in-plane AFM order exists, the magnetic point group remains compatible with inversion, so Dmetric=0 and the observed B-odd ΔV2ω cannot be assigned to the quantum metric. The B-odd signal could instead reflect skyrmion topology, field-dependent magnon or disorder contributions, or asymmetric contact/rectification effects, none of which requires a band-geometric Dmetric. The paper also provides no ab initio computation of Dmetric for TbMn6Sn6 to anchor the magnitude, sign, or temperature/field dependence of the claimed term. Thus the most load-bearing link—static P-breaking spin texture → nonzero Dmetric → observed signal—is unsupported.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports second-harmonic transport measurements in the centrosymmetric kagome magnet TbMn6Sn6 at room temperature. The authors observe a parabolic current-voltage relation for the second-harmonic voltage in two FIB-fabricated samples, split into a magnetic-field-independent offset and a field-dependent component that is odd in the applied field. They attribute the field-independent part to the Berry curvature dipole and the field-dependent part to the quantum metric dipole, arguing that a hidden in-plane antiferromagnetic Mn canting breaks both inversion and time-reversal symmetries. They further associate peaks near the spin-reorientation transition with skyrmion-induced electric magnetochiral anisotropy, and conclude that Berry curvature dipole, quantum metric dipole, and skyrmion-induced second-harmonic transport coexist at room temperature and can be tuned via magnetic fields.","tokens_in":10297,"tokens_out":7396,"duration_ms":75675,"significance":"If the quantum metric interpretation were firmly established, this would be a notable advance: a room-temperature, field-tunable nonlinear response in a centrosymmetric bulk magnet, with potential for device applications. The experimental work includes multiple samples, temperature and field dependence, parabolic I-V behavior, and some scaling analysis intended to exclude Joule heating and Drude-type impurity scattering. The paper also gives credit for addressing a topical and contested question in nonlinear transport. However, the central attribution to the quantum metric dipole rests entirely on a symmetry-breaking spin texture that is asserted rather than demonstrated, and no quantitative theoretical calculation anchors the claimed Dmetric contribution. These weaknesses currently leave the headline interpretation unsupported.","major_comments":[{"comment":"The premise that a static in-plane antiferromagnetic texture breaks inversion symmetry is not established. The 'flat-band antiferromagnetism' in ref. 17 is an inelastic neutron scattering spin-wave excitation, not a magnetic Bragg peak; it evidences dynamic correlations, not a static spin arrangement. The ~13° canting from ref. 29 is a coherent tilt of the ferrimagnetic moments, whose in-plane projection is ferromagnetic and does not itself break inversion. The magnetization data in Fig. S2 show net in-plane and out-of-plane moments that cannot distinguish a uniform canting from an alternating, inversion-breaking canting. Without a demonstrated static P-breaking texture, Dmetric = 0 in the proposed scenario, and the B-odd ΔV2ω cannot be assigned to the quantum metric.","section":"The magnetic phases in TbMn6Sn6 (paragraph beginning 'Importantly for this work')"},{"comment":"The separation of the second-harmonic signal into a field-independent offset and a T-odd field-dependent part is operational, not deductive. Subtracting V2ω(B=0) removes all field-independent contributions, but the remaining ΔV2ω could equally arise from field-modulated conductivity, contact rectification, or skyrmion dynamics. The scaling analysis said to be shown in Fig. S11 is not presented in the main text, so the reader cannot verify how well these non-geometric mechanisms are excluded. An independent calculation, a control experiment with reversed magnetic order, or a Hall-bar of different geometry is needed to attribute ΔV2ω specifically to Dmetric.","section":"Nonlinear transport at room temperature (paragraph describing subtraction of the B=0 offset)"},{"comment":"No ab initio or model calculation of Dmetric for TbMn6Sn6 is provided anywhere in the manuscript. Without a computation using the proposed spin texture, the sign, magnitude, and field/temperature dependence of the claimed quantum metric contribution are unconstrained. The statement in the abstract and conclusion that the response is 'governed by the quantum metric' therefore goes beyond what the data can support; a first-principles calculation is necessary to anchor the interpretation.","section":"Discussion and Conclusion (quantum metric paragraph)"},{"comment":"The assignment of the field-independent offset to the Berry curvature dipole is not justified. DBC can depend on magnetic field through band-structure and spin-texture changes, and the offset could contain extrinsic contributions such as contact asymmetry or thermoelectric effects. The T-even/T-odd classification alone does not determine which part arises from DBC versus other mechanisms; the text should provide an explicit symmetry analysis for the specific magnetic configuration and show why the offset is exclusively DBC.","section":"Nonlinear transport at room temperature (co-contribution model paragraph)"}],"minor_comments":[{"comment":"The phrase 'In contract' should read 'In contrast'.","section":"Introduction, first paragraph"},{"comment":"The sentence 'The anomalous conductivity is roughly a constant, and independent with the longitudinal conductivity' is ungrammatical; it should say 'independent of the longitudinal conductivity'.","section":"Electronic transport properties of TbMn6Sn6, paragraph on anomalous Hall conductivity"},{"comment":"The coefficient γ = 4V2ω/(Vω B j a.c.) is first introduced in the figure caption and later used for comparison with literature values; it should be explicitly defined and its derivation or reference stated in the main text.","section":"Discussion and Conclusion, eMChA comparison in Fig. 3C"},{"comment":"Some informal constructions, such as 'Note that' and 'Importantly for this work,' appear frequently; tightening these would improve the manuscript's formal tone.","section":"Various places"}],"recommendation":"major_revision","confidential_remarks":"The experimental dataset appears to be of good quality, and the observation of a large, field-tunable second-harmonic response near room temperature in TbMn6Sn6 is in itself interesting. My recommendation for major revision is driven by the large gap between the data and the quantum metric interpretation. To make the central claim convincing, the authors would need either to provide direct evidence for a static inversion-breaking spin texture (e.g., neutron diffraction) or to present a specific spin model with a calculated Dmetric that reproduces the observed sign, magnitude, and field dependence. If neither can be supplied, the authors should substantially reframe the manuscript as a study of field-tunable nonlinear transport without assigning the response to the quantum metric."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The measurement is probably real, but the headline interpretation is not earned yet. Two FIB-fabricated samples show parabolic second-harmonic I-V curves at 300 K, with a field-dependent component that changes sign with field direction. That is a solid experimental result, and the comparison in Fig. 3C makes a fair case that TbMn6Sn6 shows a large, tunable room-temperature nonlinear response. The authors also make a genuine effort to exclude Drude and Joule-heating artifacts. This is the first room-temperature report of this kind in a centrosymmetric magnet, and the coexistence of Berry curvature dipole, quantum metric, and skyrmion-induced contributions is a new claim.\n\nThe soft spot is the load-bearing attribution to the quantum metric. The paper needs a static, inversion-breaking in-plane antiferromagnetic texture in the Mn kagome planes. The evidence offered is a ~13° canting angle and INS features called \"flat-band antiferromagnetism.\" Neither supports a static P-breaking texture. The canting is a coherent tilt of the ferrimagnetic moments; its in-plane projection is ferromagnetic, not antiferromagnetic. The INS flat-band feature is a spin-wave excitation, not a magnetic Bragg peak; it says nothing about static order. Without static P-breaking, Dmetric is zero and the odd-in-field second-harmonic component could come from skyrmion dynamics, field-modulated conductivity, or contacts. The operational subtraction of the zero-field offset and assignment of the B-odd part to Dmetric is not backed by any quantitative calculation. No error bars are shown, and the data availability statement is the usual \"upon request.\"\n\nThis is not a fatal flaw in the experiment, but it is a serious gap between data and interpretation. The paper deserves peer review because the empirical result is significant and the interpretation is contestable. A referee should push the authors to either provide a microscopic computation of Dmetric for TbMn6Sn6 or substantially soften the quantum-metric claim. I would not cite it for the quantum-metric conclusion, but I might cite it for the measurement itself. Bring it to reading group if you want a good case study in how symmetry arguments can outrun the data.","headline":"A credible room-temperature second-harmonic transport measurement in TbMn6Sn6, but the quantum-metric attribution is inferred from symmetry and field dependence rather than demonstrated.","tokens_in":10771,"tokens_out":1962,"would_cite":false,"duration_ms":31368,"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":"In the kagome magnet TbMn6Sn6, quantum-metric-driven nonlinear transport persists and is field-tunable at room temperature.","keywords":["quantum metric","second harmonic transport","kagome magnet","TbMn6Sn6","Berry curvature dipole","spin reorientation","skyrmion","magnetochiral anisotropy"],"falsifier":"Measure the odd-in-field second-harmonic voltage in a TbMn6Sn6 crystal in which the in-plane canting is suppressed—for example, by substituting nonmagnetic Y or Lu for Tb, or by applying uniaxial pressure along the c axis—while keeping the same Hall-bar geometry: if a comparable odd-in-field $\\Delta V^{2\\omega}$ survives, the response cannot come from the quantum metric dipole activated by the hidden antiferromagnetic texture. Alternatively, rotate the magnetic field within the kagome plane with fixed magnitude and check whether the $D_{\\text{metric}}$ plateau follows the sixfold symmetry of the Mn kagome lattice; a different angular pattern would indicate a different mechanism.","tokens_in":9671,"feed_emoji":"🧲","tokens_out":6348,"duration_ms":55233,"temperature":0.7,"pith_summary":"In the kagome magnet TbMn6Sn6, the authors report a strong second-harmonic transport response that persists at room temperature and is controlled by applied magnetic fields. They attribute the field-odd part of this response to a quantum metric dipole arising from a hidden in-plane antiferromagnetic canting of the Mn moments, which breaks both inversion and time-reversal symmetry in the canted ferrimagnetic state. The same response also contains a Berry curvature dipole contribution and, near the spin-reorientation transition, a skyrmion-induced magnetochiral component. Because the spin-reorientation transition sits around 300 K, the magnetic configuration is easily switched by fields, making this one of the first quantum-geometry-driven nonlinear responses that is both tuneable and operable at practical temperatures.","feed_headline":"A kagome magnet shows tunable quantum metric effect at 300 K","feed_subtitle":"Second-harmonic transport in TbMn6Sn6 stays strong near room temperature and is switched by magnetic fields.","key_machinery":"The central object is the quantum metric dipole $D_{\\text{metric}} = \\sum_n \\int d^3k \\, g_n(\\mathbf{k}) \\, \\partial_{\\mathbf{k}} f_n$, where $g_n$ is the quantum (Fubini–Study) metric of Bloch band $n$ and $f_n$ the occupation; it produces a $T$-odd, field-odd second-harmonic response. In TbMn6Sn6, this dipole is activated by a hidden magnetic symmetry-breaking texture: within each Mn kagome plane, a flat-band antiferromagnetic pattern with an inversion-symmetric pair of Mn moments canted in opposite directions (a ~13° canting at 300 K) breaks $P$ and $T$ simultaneously. The second-harmonic transport measurement $V^{2\\omega} \\propto I^2$ is the probe; by separating the field-even Berry curvature dipole part from the field-odd quantum metric part, the authors extract the $D_{\\text{metric}}$ contribution and show it is suppressed when the field is applied in the basal plane, where the canting-induced symmetry breaking is lost. Skyrmion dynamics provide a separate, real-space contribution near the spin-reorientation region.","core_discovery":"The paper's central claim is that in the centrosymmetric kagome ferrimagnet TbMn6Sn6, the Berry curvature dipole, the quantum metric dipole, and skyrmion-induced second-harmonic transport coexist at room temperature and can be tuned by controlling the magnetic configuration. Around the spontaneous spin-reorientation transition (270–330 K), a modest magnetic field realigns the Tb and Mn moments, switching the symmetry-breaking phases on and off. The key evidence is the magnetic-field-dependent second-harmonic voltage $V_{xx}^{2\\omega}$ and $V_{xy}^{2\\omega}$: after subtracting the field-even Berry curvature dipole background, the remaining $\\Delta V^{2\\omega}$ is an odd function of field that saturates at high fields, matching a $T$-odd quantum metric dipole. A scaling analysis rules out nonlinear Drude and impurity scattering, and control measurements with in-plane fields show the response disappears, tying the effect to the symmetry of the Mn kagome planes rather than to artifacts. The authors conclude that TbMn6Sn6 is the first material showing giant, tuneable, room-temperature second-harmonic transport among the compounds compared.","pith_inferences":["If the hidden in-plane antiferromagnetic texture is confirmed by direct magnetic imaging, the same symmetry-breaking route could be sought in other centrosymmetric magnets where nonlinear transport currently appears forbidden by the lattice symmetry.","The room-temperature operation removes the cryostat bottleneck for quantum-geometry devices; a natural next step is to test rectification or terahertz detection efficiency in a TbMn6Sn6-based device at 300 K.","A clean control experiment would tune the canting angle chemically (e.g., by substituting part of the Tb or applying pressure) and check that the field-odd second-harmonic amplitude scales with the in-plane antiferromagnetic component.","The coexistence of three mechanisms at one temperature suggests that their distinct field and current dependences can be used to separate them in a single dataset, which the authors only partially exploit."],"forward_implications":["Near the spin-reorientation transition, modest magnetic fields switch the magnetic configuration, so the same device can toggle the quantum-metric and skyrmion contributions on and off at room temperature.","The field-even Berry curvature dipole and field-odd quantum metric dipole components of the second-harmonic signal can be separated by measuring $V^{2\\omega}$ at opposite fields, giving a built-in symmetry probe of hidden magnetic order.","Applying the field along the c axis activates the quantum metric response, while in-plane fields isolate the skyrmion-induced magnetochiral anisotropy, providing a route to selectively address two different nonlinear mechanisms.","Among the materials compared in the paper, TbMn6Sn6 is the only one showing giant and tunable second-harmonic transport at room temperature, a practical requirement for nonlinear electronic devices."],"supporting_citations":[{"why":"supplies the inelastic neutron scattering evidence for chiral and flat-band antiferromagnetic magnons in the Mn kagome layers.","marker":"[17]"},{"why":"reports the ~13° canting angle at 300 K that supports the in-plane antiferromagnetic component.","marker":"[29]"},{"why":"establishes the competing magnetic energy scales and spin-reorientation context of TbMn6Sn6.","marker":"[16]"},{"why":"characterizes the orbital character of the spin-reorientation transition near room temperature.","marker":"[19]"},{"why":"demonstrates the quantum metric nonlinear Hall effect and provides the extraction method used here.","marker":"[9]"},{"why":"reports quantum-metric-induced nonlinear transport in MnBi2Te4 and the scaling analysis that excludes Drude contributions.","marker":"[10]"},{"why":"provides the unified quantum-geometry description of nonlinear anomalous Hall effect and nonreciprocal magnetoresistance.","marker":"[6]"},{"why":"shows switchable chiral transport in CsV3Sb5, the cryogenic tuneable benchmark this work extends to room temperature.","marker":"[13]"},{"why":"reports room-temperature topological magnetic textures (skyrmions) in TbMn6Sn6, supporting the skyrmion eMChA contribution.","marker":"[33]"},{"why":"establishes the large Berry curvature and quantum-limit Chern magnetism in TbMn6Sn6, the band-structure basis for the Berry curvature dipole.","marker":"[37]"}],"fun_headline_variants":["Quantum metric effect switches at room temperature in kagome magnet","Room-temperature quantum metric tuned by magnetic fields in TbMn6Sn6","Tunable quantum geometry at 300 K in a kagome magnet","Kagome magnet shows field-switchable quantum metric at room temperature","First room-temperature tunable quantum metric effect in a magnet"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The entire quantum metric interpretation rests on the premise that the Mn kagome planes contain a hidden in-plane antiferromagnetic texture that breaks inversion symmetry in the canted ferrimagnetic state at room temperature.","fun_headline_variants_meta":{"raw":{"variants":["Quantum metric effect switches at room temperature in kagome magnet","Room-temperature quantum metric tuned by magnetic fields in TbMn6Sn6","Tunable quantum geometry at 300 K in a kagome magnet","Kagome magnet shows field-switchable quantum metric at room temperature","First room-temperature tunable quantum metric effect in a magnet"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000245,"raw_usage":{"total_tokens":1527,"prompt_tokens":929,"completion_tokens":598,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":545,"completion_tokens_details":{"reasoning_tokens":516}},"tokens_in":545,"tokens_out":598,"duration_ms":5414,"temperature":1.0,"reasoning_tokens":516,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-12T18:33:12.990285+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the odd-in-field second-harmonic voltage in a TbMn6Sn6 crystal in which the in-plane canting is suppressed—for example, by substituting nonmagnetic Y or Lu for Tb, or by applying uniaxial pressure along the c axis—while keeping the same Hall-bar geometry: if a comparable odd-in-field $\\Delta V^{2\\omega}$ survives, the response cannot come from the quantum metric dipole activated by the hidden antiferromagnetic texture. Alternatively, rotate the magnetic field within the kagome plane with fixed magnitude and check whether the $D_{\\text{metric}}$ plateau follows the sixfold symmetry of the Mn kagome lattice; a different angular pattern would indicate a different mechanism.","supporting_citations":[{"cited_title":"Riberolles et al., Chiral and flat-band magnetic quasiparticles in ferromagnetic and metallic kagome layers","cited_arxiv_id":null,"evidence_quote":"supplies the inelastic neutron scattering evidence for chiral and flat-band antiferromagnetic magnons in the Mn kagome layers."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"reports the ~13° canting angle at 300 K that supports the in-plane antiferromagnetic component."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"establishes the competing magnetic energy scales and spin-reorientation context of TbMn6Sn6."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"characterizes the orbital character of the spin-reorientation transition near room temperature."},{"cited_title":"Gao et al., Quantum metric nonlinear Hall effect in a topological antiferromagnetic heterostructure","cited_arxiv_id":null,"evidence_quote":"demonstrates the quantum metric nonlinear Hall effect and provides the extraction method used here."},{"cited_title":"Wang et al., Quantum-metric-induced nonlinear transport in a topological antiferromagnet","cited_arxiv_id":null,"evidence_quote":"reports quantum-metric-induced nonlinear transport in MnBi2Te4 and the scaling analysis that excludes Drude contributions."},{"cited_title":"Kaplan, T","cited_arxiv_id":null,"evidence_quote":"provides the unified quantum-geometry description of nonlinear anomalous Hall effect and nonreciprocal magnetoresistance."},{"cited_title":"Guo et al., Switchable chiral transport in charge-ordered kagome metal CsV3Sb5","cited_arxiv_id":null,"evidence_quote":"shows switchable chiral transport in CsV3Sb5, the cryogenic tuneable benchmark this work extends to room temperature."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"reports room-temperature topological magnetic textures (skyrmions) in TbMn6Sn6, supporting the skyrmion eMChA contribution."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"establishes the large Berry curvature and quantum-limit Chern magnetism in TbMn6Sn6, the band-structure basis for the Berry curvature dipole."}],"review_version":1}