{"id":"9d75b934-3931-4e73-8ce8-086085b7405d","arxiv_id":"1908.03895","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"Temperature-dependent optical conductivity of Co3Sn2S2 tracks magnetization-driven band shifts, with a fitted 1.33 energy renormalization factor, supporting the magnetic Weyl semimetal scenario.","lead":"This paper measures how the optical response of the ferromagnetic semimetal Co3Sn2S2 changes with temperature and compares it with density functional calculations at different magnetizations. It identifies which interband transitions respond to magnetization and attributes a low-energy peak to bands near Weyl nodes, supporting the magnetic Weyl semimetal picture.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The global 1.33 rescaling is load-bearing for all peak assignments, and the InterA/Weyl-node match appears to use the unscaled 310 cm^-1 position rather than the scaled 412 cm^-1 position, so the key magnetic-WSM evidence is not consistently tied to the stated renormalization.","rationale":"The reader's verdict and weakest assumption are on target. The experimental temperature-dependent optical data are internally plausible, and the qualitative evolution of InterB and InterC with magnetization is visible in the figures. My stress-test focuses on the single global rescaling factor, because every specific band assignment—including the Weyl-node-related InterA—uses it. The paper's own text around Fig. S4 creates a concrete tension: the calculated Wannier/SOC peak is quoted as ~350 cm^-1 and called consistent with the raw 310 cm^-1 InterA, while under the stated 1.33 rescaling that same experimental peak would sit at ~412 cm^-1. So either the rescaling is not global, or the InterA match is not actually part of the main comparison. This is an internal consistency issue, not a disagreement with external consensus, and it directly affects the central magnetic-WSM claim. The proposed test—reading the Fig. S4 axis and refitting a single scale factor over all three peaks—would settle whether the 1.33 factor survives or whether the InterA assignment is invalid. Until that is resolved, the conditional verdict remains appropriate; I do not recommend moving to accept or reject.","tokens_in":9075,"tokens_out":10793,"duration_ms":113364,"concrete_test":"Open the supplementary/Wannier calculation (Fig. S4 and the surrounding text) and read off the red-arrow peak energy; determine whether the stated comparison to InterA uses the raw 310 cm^-1 position or the 1.33-scaled 412 cm^-1 position. Then perform a global least-squares fit of a single scale factor s to all three peak positions (InterA, InterB, InterC) reported in the main text, and report the best s and the per-peak residuals. If the Wannier peak is aligned with the raw InterA, or if the best-fit s differs by more than ~10% between InterA and InterC, the global renormalization assumption is invalid and the InterA/Weyl-node attribution is not established.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's central inference—that optical conductivity identifies transitions from bands near the Weyl nodes (InterA) and that magnetization tunes the Weyl nodes—rests on matching calculated band-structure transition energies to measured peaks. To make that match, the experimental wavenumber axis is globally rescaled by 1.33, chosen so that InterC coincides with the calculated peak (text after Fig. 3f). This single factor is then the basis for assigning InterA, InterB, and InterC. The load-bearing weakness is that the factor is not shown to be global, and the paper's own InterA discussion provides evidence that it is not: the Wannier/SOC calculation gives a small peak 'around 350 cm^-1', said to be 'consistent with the position of InterA in Fig. 1c'. The raw InterA is at 310 cm^-1; under the 1.33 rescaling it would appear at about 412 cm^-1 on the theoretical axis. Thus the one feature that is supposed to come from the Weyl-node bands is matched either without the global rescaling (implicit factor ~1.13) or, if the rescaling is applied, with an 18% mismatch. Either way, a single global renormalization factor does not consistently connect the calculation to all three assigned peaks, and the assignment of InterA to Weyl-node bands is not supported by the comparison as written. The experimental observation of temperature-dependent peaks stands; it is the band-to-peak mapping underpinning the magnetic-WSM conclusion that is insecure.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports temperature-dependent in-plane optical conductivity measurements of Co3Sn2S2 between 5 K and 300 K, together with first-principles simulations in the paramagnetic state and in ferromagnetic states with constrained Co moments of 0.15 and 0.33 μB/Co. The authors identify three interband absorption features, InterA, InterB, and InterC, and assign them to calculated band-structure transitions: InterC is described as magnetization-insensitive, InterB as magnetization-sensitive, and InterA as arising from bands near the Weyl nodes. To obtain the assignments, the experimental wavenumber axis is rescaled by a global factor of 1.33, attributed to electron correlation, and the Drude scattering rates in the simulations are parameterized to mimic the temperature evolution. The paper concludes that Co3Sn2S2 is a magnetic Weyl semimetal and that its Weyl nodes can be tuned by magnetization and temperature.","tokens_in":9444,"tokens_out":4034,"duration_ms":46357,"significance":"If the peak assignments and the band-resolved interpretation are correct, the work would provide a clear optical-spectroscopy signature of magnetization-driven band shifts in a magnetic Weyl semimetal candidate, and would add quantitative evidence about the strength of electron correlation in Co3Sn2S2. The experimental data are careful and internally consistent: the extrapolated dc conductivity matches transport data, the spectral-weight analysis is physically reasonable, and the observation of temperature-dependent interband features is robust. However, the two quantitative pillars of the paper, namely the global 1.33 renormalization factor and the identification of InterA with Weyl-node-related transitions, are not established with sufficient rigor, and the constrained-moment calculations rely on parameters chosen to match the data. These issues do not invalidate the raw experimental findings, but they currently prevent the paper from supporting the strong claims in the abstract.","major_comments":[{"comment":"The global rescaling of the experimental wavenumber axis by a factor of 1.33 is introduced specifically to match the calculated position of InterC, and the same rescaling is then used to claim that electron correlation in Co3Sn2S2 is moderate. This argument is partly circular: the renormalization factor is fitted to one peak and is not derived from any independent many-body calculation, and no uncertainty is attached to any of the three peak positions. A quantitative demonstration that the same factor consistently aligns InterA, InterB, and InterC, with stated tolerances, is required before the conclusion about moderate correlation can be accepted.","section":"Fig. 3f and text after it"},{"comment":"The assignment of InterA (310 cm−1) to transitions between bands near the Weyl nodes is not consistent with the stated rescaling. The manuscript says that the Wannier/SOC calculation gives a peak around 350 cm−1 that is consistent with the position of InterA in Fig. 1c, but on the rescaled abscissa used in Fig. 3f the measured 310 cm−1 feature would appear near 412 cm−1, which is an 18 percent discrepancy. Thus the comparison either ignores the 1.33 rescaling or, if the rescaling is applied, the match is poor. In either case a single global renormalization factor does not consistently support all three peak assignments, and the identification of InterA with Weyl-node-related transitions is not established.","section":"Discussion of InterA, p. 4"},{"comment":"The constrained Co moments of 0.15 and 0.33 μB/Co are chosen to mimic the 100 K and 5 K states, but no independent relationship between temperature and magnetic moment is given. Without such a link, the comparison between experimental spectra and calculations at different fixed moments only demonstrates that the data can be reproduced by tuning two additional parameters; it does not by itself prove that the temperature-induced band shift is driven by magnetization. The authors should connect the constrained moments to measured magnetization values or to a temperature-dependent moment from first-principles or experiment.","section":"Sec. on first-principles simulations"},{"comment":"The simulated spectra are generated with Drude scattering rates of 0.17, 0.05, and 0.03 eV, selected to match the experimental spectra. Because these choices affect the visibility of low-energy interband structure, the assertion that InterA is present below 100 K but cannot be resolved in the calculated spectra should be tested by varying the Drude parameters and by checking the robustness of the low-energy peak, rather than made on the basis of a single set of fitted scattering rates.","section":"Fig. 3f and simulated Drude parameters"}],"minor_comments":[{"comment":"The manuscript contains several typographical errors, including 'tow-dimensional' in the introduction and 'repspectively' in the discussion of Fig. 3, which should be corrected in a revised version.","section":"Throughout"},{"comment":"The parameters of the Drude-Lorentz fits used in Eq. (1) are not reported; a table listing the plasma frequencies, scattering rates, oscillator positions, widths, and strengths for the temperatures shown would improve reproducibility and allow readers to judge the quality of the fits.","section":"Eq. (1) and Fig. 2"},{"comment":"The claim that the ω-linear conductivity from 130 to 230 cm−1 indicates the presence of 3D linear bands would be more convincing if accompanied by a quantitative comparison with the calculated joint density of states in the corresponding energy range, rather than only a linear extrapolation.","section":"Fig. 2b and text on ω-linear conductivity"},{"comment":"The phrase 'the results strongly support that Co3Sn2S2 is a magnetic WSM' is too strong relative to the evidence presented, which is based on peak assignments with the fitted rescaling; the wording should be moderated to reflect the assumptions involved.","section":"Abstract and summary"}],"recommendation":"major_revision","confidential_remarks":"The experimental optical data and the observation of temperature-dependent spectral changes appear sound and may be a useful contribution. However, the central band-to-peak assignments and the 1.33 renormalization claim rest on a fitted rescaling that is internally inconsistent for InterA, and the constrained-moment simulations are not independently linked to temperature. Major revision with a reanalysis of all three peaks on a common energy scale, explicit treatment of the rescaling and its uncertainty, and a clear link between moments and temperature is needed before the manuscript can be considered for publication."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Run Yang et al. report a careful temperature-dependent optical conductivity study of Co3Sn2S2 from 20 to 7000 cm^-1. That dataset is the real contribution: clear Drude-Lorentz evolution, spectral weight transfer below TC, a sharp plasma edge and suppressed Drude weight below 100 K, and a ω-linear conductivity tail over 130-230 cm^-1 that they associate with linear bands. The qualitative temperature dependence is visible in the figures and internally consistent. The paper also makes a plausible case that the mid-infrared peaks InterB and InterC behave differently with magnetization, with InterC nearly T-independent and InterB appearing only in the ferromagnetic state. That part is worth a serious look.\n\nThe soft spot is the quantitative mapping between theory and experiment. The experimental wavenumber axis is scaled by a factor of 1.33, chosen so that InterC lines up with the calculated peak. That single factor is then used to support the claim of moderate correlation and to assign InterA, InterB and InterC. But the same paper says the Wannier calculation gives a small peak 'around 350 cm^-1' that is 'consistent with the position of InterA' at 310 cm^-1. Under the 1.33 rescaling, InterA would sit near 412 cm^-1, an 18% mismatch with the calculated 350. So the one peak attributed to the Weyl-node bands is matched either with a different implicit rescaling (~1.13) or not at all. The global 1.33 factor is load-bearing, and this is direct evidence that it is not actually global.\n\nThere are secondary concerns, all in the same direction: the constrained magnetic moments 0.15 and 0.33 μB/Co are chosen to represent 100 K and 5 K without a temperature-to-moment link, and the Drude scattering rates in the simulated spectra are parameterized to fit. No error bars or raw data are included. None of this kills the experimental observation, but it means the paper's closing claim—that the results strongly support Co3Sn2S2 as a magnetic Weyl semimetal with tunable Weyl nodes—is much weaker than the abstract suggests.\n\nWho is this for? It is useful for people working on Co3Sn2S2, magnetic Weyl semimetals, or optical spectroscopy of correlated metals. It deserves a serious referee: the measurement is valuable, and the paper's internal inconsistency needs to be resolved by revision, not by desk rejection. I'd send it to review with a request that the authors present the InterA match honestly and state clearly what is fitted versus predicted. Would I cite it? Only if I were working on this exact material.","headline":"Solid optical dataset, but the Weyl-node peak assignment depends on a global 1.33 rescaling that the paper's own numbers contradict.","tokens_in":9947,"tokens_out":2640,"would_cite":false,"duration_ms":27359,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["72.15.-v","74.70.-b","78.30.-j"],"model":"deepseek-v4-flash","headline":"Temperature-dependent optical spectra reveal magnetization-driven band shifts in the ferromagnetic Weyl semimetal candidate Co3Sn2S2 and identify a low-energy transition tied to its Weyl nodes.","keywords":["Weyl semimetal","Co3Sn2S2","optical conductivity","band renormalization","exchange splitting","magnetic phase transition","Drude-Lorentz analysis","first-principles calculation"],"falsifier":"Measure the actual electronic bands of Co3Sn2S2 with angle-resolved photoemission at 5 K and 100 K and compare them with the density functional theory bands computed at moments of 0.33 and 0.15 Bohr magnetons per Co; if different bands need different rescaling factors rather than one global 1.33, the assignments of InterA, InterB, and InterC collapse. Alternatively, apply a magnetic field at fixed temperature near the Curie temperature: if the 310 cm-1 InterA peak does not shift in position or weight as magnetization grows, the Weyl-node attribution is not supported.","tokens_in":8885,"feed_emoji":"🧲","tokens_out":11838,"duration_ms":121594,"temperature":0.7,"pith_summary":"The paper sets out to show that Co3Sn2S2 is a magnetic Weyl semimetal whose Weyl nodes move as the magnetization changes, and that optical spectroscopy can observe that movement directly. It measures the optical conductivity from 300 K down to 5 K and compares the spectra with first-principles band structures computed with the Co moment constrained to values meant to represent the paramagnetic, 100 K, and 5 K states. After rescaling the experimental photon-energy axis by a factor of 1.33, the three observed interband peaks line up with specific calculated transitions, including a low-energy peak from spin-orbit-gapped bands near the Weyl nodes. A careful reader would care because a magnetic Weyl semimetal with magnetization-tunable Weyl nodes offers a practical temperature or magnetic-field knob on topological electronic properties.","feed_headline":"A 1.33 rescaling exposes magnetization-tunable Weyl bands in Co3Sn2S2","feed_subtitle":"Infrared spectra plus first-principles calculations pin three interband peaks and tie the lowest one to the Weyl nodes.","key_machinery":"The load-bearing object is the magnetization-constrained first-principles band structure. The calculations hold the Co magnetic moment fixed at zero, 0.15, and 0.33 Bohr magnetons per Co to represent the paramagnetic, 100 K, and 5 K states, and the exchange splitting between spin channels is what shifts the bands. The optical conductivity is computed from the Kubo formula and compared with measurement after rescaling the experimental photon wavenumber by 1.33; the same rescaling is then used to attribute the observed peaks to calculated interband transitions. The linear-in-frequency optical conductivity below 100 K and the sharp plasma edge are the signatures used to tie InterA to three-dimensional linear bands near the Weyl nodes.","core_discovery":"The paper's central claim is that the temperature evolution of Co3Sn2S2's optical conductivity is the optical fingerprint of magnetization-driven band shifts, not just thermal broadening. As the material cools below its Curie temperature near 177 K, exchange splitting separates the spin-up and spin-down bands, with the spin-up bands moving toward the Fermi level and the spin-down bands moving to higher energy. Comparing the measured spectra with density functional theory at constrained moments assigns the three interband peaks: InterC, insensitive to magnetization and arising from crystal-field-split Co 3d t2g/eg bands; InterB, which appears only after the magnetic transition and comes from same-spin-channel Co 3d transitions; and InterA near 310 cm-1, which comes from the bands gapped by spin-orbit coupling along the nodal line and surrounding the Weyl nodes. The paper further argues that the single 1.33 rescaling means electron correlation is moderate, and that the $T^2$ suppression of the Drude weight below 100 K matches the theoretical expectation for a Weyl semimetal. The asserted conclusion is that Co3Sn2S2 is a magnetic Weyl semimetal and its Weyl nodes can be tuned by magnetization through temperature change.","pith_inferences":["At fixed temperature below the Curie temperature, an applied magnetic field should shift and reshape InterA and InterB by changing the net magnetization; the paper does not test this field dependence, and it would provide a direct confirmation of the magnetization-tuning claim.","The single-factor 1.33 renormalization suggests that other cobalt-based shandites with similar Co 3d character might show the same global rescaling; checking that would reveal whether the moderate-correlation picture is specific to Co3Sn2S2 or generic to the family.","If the constrained moments truly represent the 100 K and 5 K states, then the measured temperature-dependent peak positions effectively map out the temperature dependence of the local Co moment, allowing optical data to be inverted into a magnetization curve.","The paper suggests a Lifshitz transition below 100 K as parabolic bands move away from the Fermi level; a search for this transition in quantum oscillation or thermoelectric measurements would be a testable consequence beyond the optical data."],"forward_implications":["If the identification is right, the position and strength of the 310 cm-1 InterA peak track the spin-orbit-gapped bands that form the Weyl nodes, so bulk optical measurements can report on Weyl-node formation without surface-sensitive probes.","Because one global 1.33 rescaling reproduces three peaks, the correlation correction in Co3Sn2S2 is a moderate, mostly momentum-independent renormalization, making density functional theory band assignments reliable for this material.","The $T^2$ suppression of the Drude weight below 100 K, if caused by Weyl physics, gives a simple optical and transport signature for recognizing magnetic Weyl semimetals.","The magnetization-sensitive InterB appears only below the magnetic transition, so its onset marks the ferromagnetic phase in optical data.","If the Weyl nodes move with magnetization, then temperature or magnetic field can be used to tune the anomalous Hall response and related topological properties in this compound."],"supporting_citations":[{"why":"Establishes Co3Sn2S2 as a ferromagnet with strong anomalous Hall effect and low carrier density, setting up the candidate material and the phenomena the paper studies.","marker":"[1]"},{"why":"Provides the band-structure picture of nodal rings and magnetization-dependent Weyl-node positions that the optical spectra are compared against.","marker":"[2]"},{"why":"Reports first-principles three-pair Weyl points below the magnetic transition and their evolution with magnetization, the specific target of the optical identification.","marker":"[3]"},{"why":"Supplies the Drude-Lorentz and Kubo formalism used to fit the measured optical conductivity and to simulate interband transitions from the calculated bands.","marker":"[12]"},{"why":"Shows that a linear-in-frequency optical conductivity marks three-dimensional linear bands, the basis for reading the low-energy response as evidence of Weyl-node bands.","marker":"[18]"},{"why":"Gives the standard framework for identifying optical and transport signatures of Weyl semimetals, including the role of linear bands and selection rules.","marker":"[20]"},{"why":"Predicts a $T^2$ temperature dependence of the Drude weight in Weyl semimetals, which the paper matches with the measured suppression below 100 K.","marker":"[30]"}],"fun_headline_variants":["Magnetization tunes Weyl bands in Co3Sn2S2, optics reveal","Temperature shifts Weyl bands in Co3Sn2S2 via magnetization","Optical spectra show magnetization-tunable Weyl bands in Co3Sn2S2","Optical probe of magnetization-tuned Weyl nodes in Co3Sn2S2"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The peak assignments depend on the assumption that a single factor of 1.33 uniformly rescales all calculated bands to match experiment, and that the two constrained Co moments faithfully represent the 100 K and 5 K states.","fun_headline_variants_meta":{"raw":{"variants":["Magnetization tunes Weyl bands in Co3Sn2S2, optics reveal","Temperature shifts Weyl bands in Co3Sn2S2 via magnetization","Optical spectra show magnetization-tunable Weyl bands in Co3Sn2S2","Optical probe of magnetization-tuned Weyl nodes in Co3Sn2S2"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001373,"raw_usage":{"total_tokens":5618,"prompt_tokens":1054,"completion_tokens":4564,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":670,"completion_tokens_details":{"reasoning_tokens":4475}},"tokens_in":670,"tokens_out":4564,"duration_ms":32849,"temperature":1.0,"reasoning_tokens":4475,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-14T13:58:54.769637+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the actual electronic bands of Co3Sn2S2 with angle-resolved photoemission at 5 K and 100 K and compare them with the density functional theory bands computed at moments of 0.33 and 0.15 Bohr magnetons per Co; if different bands need different rescaling factors rather than one global 1.33, the assignments of InterA, InterB, and InterC collapse. Alternatively, apply a magnetic field at fixed temperature near the Curie temperature: if the 310 cm-1 InterA peak does not shift in position or weight as magnetization grows, the Weyl-node attribution is not supported.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Reports first-principles three-pair Weyl points below the magnetic transition and their evolution with magnetization, the specific target of the optical identification."},{"cited_title":"Dressel and G","cited_arxiv_id":null,"evidence_quote":"Supplies the Drude-Lorentz and Kubo formalism used to fit the measured optical conductivity and to simulate interband transitions from the calculated bands."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Shows that a linear-in-frequency optical conductivity marks three-dimensional linear bands, the basis for reading the low-energy response as evidence of Weyl-node bands."}],"review_version":1}