{"id":"7d2fe71a-76a6-4e7b-8217-cb4ab3200b6b","arxiv_id":"2605.29297","paper_version":1,"verdict":"UNVERDICTED","confidence":"LOW","novelty_score":6.0,"correctness_risk":"unknown","formal_verification":"none","parameter_count":0,"one_line_summary":"In YCo3 the anomalous Nernst coefficient reverses sign near 100 K due to a temperature-driven topological Lifshitz transition that moves the Fermi level relative to Weyl nodes.","lead":"The study reports that the anomalous Nernst effect in kagome magnet YCo3 reverses sign with temperature due to a shift in electronic band topology. This could enable magnetic control of thermoelectric polarity in devices such as thermopiles.","discovery_kind":"new_application","skeptic_critique":{"model":"grok-4.3","headline":"Interpretation of ANE sign reversal as Lifshitz transition at Weyl nodes rests on DFT accurately locating nodes and modeling E_F shift from Co moment evolution","rationale":"The reader’s weakest assumption directly identifies the same load-bearing step—the correctness of the DFT placement of Weyl nodes and the Fermi-level shift. No additional internal inconsistency appears in the abstract-level claim, and the paper presents the Lifshitz scenario as an interpretation rather than a proven mechanism. Therefore the UNVERDICTED status is unchanged pending verification of the calculations.","tokens_in":1803,"tokens_out":386,"duration_ms":32708,"concrete_test":"From the paper’s DFT section or SI, extract the calculated positions of the nearest Weyl nodes relative to E_F at the magnetization value corresponding to 100 K; recompute or inspect the shift in E_F when Co moment is varied by the experimental ΔM between 50 K and 150 K. If no node crosses E_F or no Lifshitz feature appears within 50 meV of the transition, the topological interpretation does not hold.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim requires that first-principles calculations place Weyl nodes near E_F such that the observed ~100 K change in Co moments induces a Lifshitz transition (node crossing or van Hove feature) that flips the ANE sign while producing the piecewise-linear AHC slope change. DFT band positions carry typical errors of 0.1–0.5 eV; if the calculated nodes lie more than ~kT away from E_F or if moment-induced shifts do not cross a node at the experimental temperature, the topological assignment fails and extrinsic scattering or unrelated band evolution remain viable. The abstract states the anomalies “could be interpreted” this way, but the link is only as strong as the unverified node positions and shift magnitude.","agreement_with_reader":"agree"},"referee_report":{"model":"grok-4.3","summary":"The manuscript reports experimental observation of sizable anomalous Hall and Nernst effects below TC ~ 225 K in the kagome magnet YCo3. The anomalous Hall conductivity shows a piecewise-linear dependence on magnetization with an abrupt slope change near 100 K, while the anomalous Nernst coefficient SAyx reverses sign at the same temperature. First-principles calculations are invoked to argue for an intrinsic (Karplus-Luttinger) mechanism, and the anomalies are suggested to arise from a temperature-induced topological Lifshitz transition in which Co-moment evolution shifts the Fermi level relative to Weyl nodes.","tokens_in":1967,"tokens_out":545,"duration_ms":27683,"significance":"If the topological assignment holds, the result would demonstrate direct magnetic control over the sign of the anomalous Nernst effect via a Lifshitz transition in a kagome system, offering a route to bipolar thermoelectric response. The combination of transport data with DFT band-structure input is a standard approach in the field, but the strength of the conclusion rests entirely on the accuracy of the calculated node positions and moment-induced shifts.","major_comments":[{"comment":"The central claim that the observed ~100 K anomalies constitute a Lifshitz transition at Weyl nodes is load-bearing for the title and abstract interpretation. The manuscript must supply the calculated energies of the relevant Weyl nodes relative to EF together with the magnitude of the EF shift induced by the measured change in Co moment between 50 K and 150 K; without these numbers it is impossible to verify that a node crossing or van-Hove feature occurs on the experimental temperature scale.","section":"Discussion / first-principles section"},{"comment":"Typical DFT errors in absolute band positions are 0.1–0.5 eV. The paper should therefore test the robustness of the Lifshitz assignment by shifting the calculated Fermi level or node energies within this window and showing that the sign reversal and slope change remain consistent with the data only for the reported node placement.","section":"Discussion"}],"minor_comments":[{"comment":"The abstract uses the cautious phrasing “could be interpreted”; the main text should maintain the same level of qualification when stating the Lifshitz scenario.","section":"Abstract"},{"comment":"Figure captions and axis labels for the temperature-dependent SAyx and σxy data should explicitly state the measurement geometry and the definition of the anomalous Nernst coefficient to avoid ambiguity with the ordinary Nernst term.","section":"Figures"}],"recommendation":"major_revision","confidential_remarks":null},"author_rebuttal":{"model":"grok-4.3","summary":"We thank the referee for the detailed and constructive report. The two major comments correctly identify that the manuscript currently lacks explicit numerical values for the Weyl-node energies and the moment-induced Fermi-level shift, as well as a robustness test against typical DFT uncertainties. We address both points below and will revise the manuscript accordingly.","responses":[{"response":"We agree that the absence of these explicit numbers weakens the quantitative support for the Lifshitz-transition interpretation. In the revised manuscript we will report the DFT-computed energies of the relevant Weyl nodes relative to EF together with the calculated Fermi-level shift arising from the measured change in Co moment between 50 K and 150 K, thereby allowing direct verification that the crossing occurs on the experimental temperature scale.","revision_made":"yes","referee_comment":"[Discussion / first-principles section] The central claim that the observed ~100 K anomalies constitute a Lifshitz transition at Weyl nodes is load-bearing for the title and abstract interpretation. The manuscript must supply the calculated energies of the relevant Weyl nodes relative to EF together with the magnitude of the EF shift induced by the measured change in Co moment between 50 K and 150 K; without these numbers it is impossible to verify that a node crossing or van-Hove feature occurs on the experimental temperature scale."},{"response":"We acknowledge that typical DFT errors must be addressed. In the revision we will add a robustness analysis in which the Fermi level (or node energies) is shifted by ±0.1–0.5 eV; we will demonstrate that the qualitative features of the anomalous-Hall slope change and Nernst sign reversal remain consistent with experiment only when the nodes are placed near the reported position.","revision_made":"yes","referee_comment":"[Discussion] Typical DFT errors in absolute band positions are 0.1–0.5 eV. The paper should therefore test the robustness of the Lifshitz assignment by shifting the calculated Fermi level or node energies within this window and showing that the sign reversal and slope change remain consistent with the data only for the reported node placement."}],"tokens_in":1486,"tokens_out":458,"duration_ms":20122,"standing_objections":[]},"desk_editor":{"model":"grok-4.3","letter":"The main point is an experimental report of bipolar anomalous Nernst effect in YCo3, with the sign change tied to a temperature around 100 K that also affects the Hall conductivity slope.\n\nThe authors measure sizable AHE and ANE below Tc of 225 K. They use first-principles work to argue the effects are intrinsic. The Hall conductivity versus magnetization is piecewise linear, with a break near 100 K that matches the Nernst sign flip. They suggest this comes from a Lifshitz transition as Co moments evolve and move the Fermi level past Weyl nodes.\n\nWhat stands out is the temperature control of the polarity, which could matter for thermoelectric applications. The data support an intrinsic mechanism reasonably well, and the Karplus-Luttinger consistency is a plus.\n\nThe weaker part is the topological assignment. It hinges on the calculations putting the nodes in the right place for the observed moment change to trigger the transition. Typical DFT shifts and positioning errors could easily move things by 0.1 eV or more, which is enough to break the story if the nodes are not that close. The paper phrases it as a possible interpretation, so they are not overclaiming, but the evidence for the mechanism is indirect.\n\nThis paper is aimed at groups studying kagome lattices and magnetic topological transport. Someone working on similar materials would find the transport data useful to compare against.\n\nThe experimental results are solid enough to merit referee attention, even if the interpretation needs tightening. I would recommend sending it for review.","headline":"The paper reports a temperature-driven sign flip in the anomalous Nernst coefficient of YCo3 near 100 K that tracks a slope change in anomalous Hall conductivity, with the link to a Lifshitz transition resting on DFT node placement.","tokens_in":2509,"tokens_out":406,"would_cite":false,"duration_ms":52956,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"grok-4.3","headline":"Temperature-driven Lifshitz transition reverses the anomalous Nernst sign in YCo3","keywords":["kagome magnet","anomalous Nernst effect","topological Lifshitz transition","Weyl nodes","YCo3","anomalous Hall conductivity","bipolar thermoelectric"],"falsifier":"ARPES data or refined calculations showing the Fermi level does not cross a Weyl node near 100 K while the sign reversal still occurs, or the reversal vanishing when magnetization is held fixed.","tokens_in":2705,"feed_emoji":"🧲","tokens_out":500,"duration_ms":23514,"temperature":0.7,"pith_summary":"The paper shows that in the kagome magnet YCo3 the anomalous Nernst coefficient changes sign near 100 K as temperature rises. This reversal arises because the evolving magnetic moments on cobalt atoms shift the Fermi level across Weyl nodes in the band structure, triggering a topological Lifshitz transition. A sympathetic reader would care because sign reversal enables bipolar thermoelectric devices that can be controlled by magnetism rather than external fields. The intrinsic nature of the effect is supported by the piecewise linear dependence of anomalous Hall conductivity on magnetization and by first-principles calculations.","feed_headline":"Anomalous Nernst sign flips in YCo3 via Lifshitz transition","feed_subtitle":"Temperature evolution of Co moments shifts Fermi level across Weyl nodes, producing bipolar response below 225 K Curie point.","key_machinery":"Topological Lifshitz transition: a change in Fermi-surface topology when temperature-tuned magnetization moves the Fermi level across Weyl nodes.","core_discovery":"The central claim is that the bipolarity of the anomalous Nernst effect in YCo3, manifested as the sign reversal of the anomalous Nernst coefficient SAyx around 100 K, results from a temperature-induced topological Lifshitz transition. This transition is enabled by the temperature evolution of Co moments that shift the Fermi level relative to the Weyl nodes. The anomalous Hall and Nernst effects are dominated by the intrinsic mechanism, with the anomalous Hall conductivity showing a piecewise-linear dependence on magnetization consistent with the Karplus-Luttinger mechanism.","pith_inferences":[],"forward_implications":[],"fun_headline_variants":["YCo3 ANE sign reversal triggered by Lifshitz transition","Topological Lifshitz transition yields bipolar ANE in YCo3","ANE polarity flips in YCo3 due to Fermi level shift","Kagome YCo3 shows temperature-induced ANE sign change"],"cache_read_input_tokens":2112,"weakest_assumption_plain":"The first-principles calculations correctly locate the Weyl nodes and Fermi level so their relative motion with temperature produces the observed sign reversal rather than extrinsic scattering or unrelated band evolution.","fun_headline_variants_meta":{"raw":{"variants":["YCo3 ANE sign reversal triggered by Lifshitz transition","Topological Lifshitz transition yields bipolar ANE in YCo3","ANE polarity flips in YCo3 due to Fermi level shift","Kagome YCo3 shows temperature-induced ANE sign change"]},"model":"grok-4.3","cost_usd":0.00659,"raw_usage":{"total_tokens":3122,"prompt_tokens":757,"num_sources_used":0,"completion_tokens":73,"cost_in_usd_ticks":65899500,"prompt_tokens_details":{"text_tokens":757,"audio_tokens":0,"image_tokens":0,"cached_tokens":256},"completion_tokens_details":{"audio_tokens":0,"reasoning_tokens":2292,"accepted_prediction_tokens":0,"rejected_prediction_tokens":0}},"tokens_in":757,"tokens_out":73,"duration_ms":22366,"temperature":1.0,"reasoning_tokens":2292,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-06-29T07:00:13.780490+00:00","model_set":{"reader":"grok-4.3"},"falsifier":"ARPES data or refined calculations showing the Fermi level does not cross a Weyl node near 100 K while the sign reversal still occurs, or the reversal vanishing when magnetization is held fixed.","supporting_citations":[],"review_version":1}