{"id":"303641e9-d350-474b-af72-b0d614be06ab","arxiv_id":"2508.12985","paper_version":1,"verdict":"UNVERDICTED","confidence":"LOW","novelty_score":6.0,"correctness_risk":"unknown","formal_verification":"none","parameter_count":0,"one_line_summary":"Co1/4TaSe2 is reported to be a layered altermagnet with a Neel temperature of 178 K, showing spin-split electronic bands observed by ARPES and matching DFT calculations.","lead":"Experiments identify a layered compound, Co1/4TaSe2, as an altermagnet, a magnetic phase with no net magnetization but spin-split electronic bands. The material orders at 178 K, which is relatively high for a layered altermagnet and could make it useful for spintronics.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Because the supplied full text is corrupted, the altermagnetic interpretation of the ARPES splitting cannot be checked; the weakest link is excluding non-altermagnetic origins of the observed band splitting.","rationale":"The reader's verdict is UNVERDICTED because the full text is corrupted, and my review of the available material reaches the same conclusion. The abstract alone is not enough to establish the central claim: the susceptibility measurement indicates type-A AFM order, but the step from that magnetic order to the ARPES band splitting being altermagnetic depends on the DFT magnetic ground state and on excluding other band-degeneracy mechanisms. The supplied full text is not merely garbled; it contains unrelated content, including an arXiv identifier for a different stat.ME paper and a GitHub link, so no methods, figures, or supporting analysis can be inspected. I do not interpret this as evidence of misconduct—only as a reason the manuscript cannot currently be evaluated. The reader's weakest assumption correctly identifies the interpretive load on the DFT magnetic ground state and the exclusion of alternative mechanisms. Since my concern is a verifiability gap rather than a demonstrated flaw, the appropriate verdict remains UNVERDICTED, unchanged from the reader's assessment.","tokens_in":32950,"tokens_out":2121,"duration_ms":25055,"concrete_test":"Run a clean-copy check of the Methods and Figures: determine whether ARPES was spin-resolved. If it was unpolarized, the decisive test is a quantitative comparison of the measured constant-energy maps along the predicted altermagnetic k-paths with (i) DFT bands for the proposed type-A order and (ii) a nonmagnetic+SOC calculation. If the nonmagnetic+SOC calculation reproduces the same splitting to within experimental resolution, the altermagnetic assignment is not supported; if only the AFM calculation matches, the concern is answered.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim—Co1/4TaSe2 shows altermagnetic spin splitting—requires that the band splitting seen in ARPES is caused by the proposed type-A antiferromagnetic order. The abstract reports unpolarized ARPES band structure in 'excellent agreement' with DFT, plus temperature-dependent gap closure above TN. But an unpolarized ARPES map cannot by itself distinguish spin splitting from an accidentally doubled band, a surface state, or spin-orbit splitting; the interpretation depends entirely on the DFT magnetic ground state being the true one. Since the manuscript body is unreadable (it contains pages from an unrelated stat.ME article), I cannot verify that the methods included spin-resolved ARPES, symmetry analysis, or a comparison against nonmagnetic/SOC calculations. That is a verifiability failure, not a demonstrated error; the science may be correct, but the evidence is unavailable.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript (arXiv:2508.12985) claims that Co1/4TaSe2 is a layered altermagnet: magnetic susceptibility indicates type-A antiferromagnetic order with a Néel temperature of 178 K, and ARPES measurements, compared with DFT calculations, are reported to show altermagnetic spin splitting at the Fermi surface. Temperature-dependent ARPES is also claimed to show band shifts and gap closure above TN, attributed to suppression of altermagnetic order. Only the abstract is readable; the supplied full text is a corrupted sequence of pages from an unrelated arXiv:2508.12983v2 (stat.ME) submission, so none of the experimental, computational, or analytical details can be examined.","tokens_in":33241,"tokens_out":3879,"duration_ms":39436,"significance":"If correct, the reported observation would add a new layered altermagnet with a relatively high Néel temperature and provide an ARPES-based signature of altermagnetic spin splitting, a topic of current interest. The combination of susceptibility, DFT, and ARPES is well suited to this problem. However, the unreadable full text means that the evidence for every central claim—magnetic structure determination, ARPES band assignments, comparison methodology, and the temperature-dependent analysis—is unavailable. I therefore cannot evaluate whether the support is sufficient, and the manuscript in its current form is not reviewable.","major_comments":[{"comment":"The body of the manuscript is not the paper described in the abstract. It consists of garbled pages from arXiv:2508.12983v2, an unrelated statistics paper, including its title, author email, and GitHub URL (e.g., 'https://github.com/PsychometricsMZ/dsem_tutorial'). This is a verifiability failure: the susceptibility measurements, ARPES data and fitting, DFT calculations, symmetry analysis, and temperature-dependent analysis are all absent. The central claim of altermagnetic spin splitting cannot be checked. The authors must resubmit a legible version of the intended manuscript.","section":"Full Text (entire manuscript body)"},{"comment":"The abstract reports 'clear signatures of altermagnetic spin splitting at the Fermi surface' but does not state that spin-resolved ARPES was performed. Unpolarized ARPES shows dispersion, not spin polarization; assigning a band splitting to altermagnetism requires ruling out Rashba-type spin-orbit splitting, surface states, or accidental band overlap, and ideally direct spin-resolved detection or spin-polarized calculations. Please clarify the experimental and theoretical evidence and provide the relevant figures and analysis in the corrected manuscript.","section":"Abstract (ARPES interpretation)"},{"comment":"The claim of band shifts and gap closure above TN is central to the altermagnetic interpretation, but the abstract gives no quantitative information: no fitted gap energies, no error bars, no comparison with instrumental resolution, and no data at intermediate temperatures. This analysis must be presented in full before the claim can be evaluated.","section":"Abstract (temperature dependence)"}],"minor_comments":[{"comment":"The abstract uses 'Neel' where 'Néel' is the correct spelling; this should be corrected throughout.","section":"Abstract"},{"comment":"The abstract would benefit from specifying the ARPES photon energy and measurement temperature, and the DFT functional and magnetic model used; these details likely belong in the intended full text.","section":"Abstract"}],"recommendation":"major_revision","confidential_remarks":"The manuscript file appears to be a submission error: the body is an unrelated statistics paper. The editor may wish to contact the authors before sending the paper out again. If a corrected PDF is not provided, I would recommend rejection rather than attempting to review the abstract alone."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Quick take: this is a paper I can't evaluate, because the file I got is mostly a corrupted text dump, including pages from an unrelated stat.ME preprint. Only the abstract is legible. So the verdict has to be: not reviewable as submitted.\n\nThe abstract makes a real claim: Co1/4TaSe2 is a layered altermagnet with type-A AFM order, TN = 178 K, and ARPES shows spin-split bands that disappear above TN. If the claim holds up, it would add one of the few experimentally verified layered altermagnets with a fairly high Neel temperature, and that matters to the altermagnetism and spintronics community. The design of the experiments is sensible: susceptibility to pin the magnetic ordering, DFT to predict the band structure, ARPES to look for the predicted splitting, and temperature-dependent ARPES to tie the splitting to the magnetic transition. The authors frame it as an identification of a new material, which is a fair framing given how few such compounds have been verified.\n\nThe soft spot is not the physics, on the evidence I have: it is that I don't have the evidence. The full text is unreadable. No methods, no figures, no error bars, no references. That alone blocks any serious assessment. On top of that, even the abstract contains the usual gap: unpolarized ARPES cannot distinguish an altermagnetic spin splitting from an accidentally doubled band, a surface state, or a spin-orbit splitting. The interpretation rests on the DFT magnetic ground state being the true one. That is a standard caveat in this literature, not a fatal flaw, but the paper would need spin-resolved data or a careful symmetry analysis to close it. The abstract doesn't mention either.\n\nWho is this for: the subfield of altermagnetism, especially people working on layered TMD intercalates and spintronics. If the authors supply a clean manuscript, it should go to peer review; the claim is important enough to warrant referee time. But I would not accept or cite this version. My recommendation to you: ask for the clean PDF, then send it out. Don't let the corrupted file be the reason the claim dies, but don't treat the abstract as evidence.","headline":"Plausible new layered altermagnet claim that is unverifiable as submitted because the manuscript body is a corrupted text dump; I can't judge the science, but if a clean version exists it deserves peer review.","tokens_in":33663,"tokens_out":2982,"would_cite":false,"duration_ms":31563,"reading_group":"maybe","serious_thinker":"unclear","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"This paper identifies Co1/4TaSe2 as a layered altermagnet and reports photoemission evidence of spin splitting that disappears above its 178 K Néel temperature.","keywords":["altermagnetism","spin splitting","ARPES","density functional theory","transition metal dichalcogenide","antiferromagnetism","Co1/4TaSe2","Néel temperature"],"falsifier":"Measure the spin polarization of the split Fermi-surface sheets with spin-resolved ARPES: altermagnetism requires the two sheets to carry opposite spin polarization that reverses across the antiferromagnetic sublattices. Alternatively, neutron diffraction that finds a different magnetic propagation vector, or observation that the splitting persists well above 178 K, would disprove the claim.","tokens_in":32800,"feed_emoji":"🧲","tokens_out":2937,"duration_ms":28661,"temperature":0.7,"pith_summary":"This paper claims that Co1/4TaSe2 is a layered altermagnetic material: a magnetically ordered state with zero net magnetization whose electronic bands still split by spin direction. Using angle-resolved photoemission spectroscopy and density functional theory, the authors report band splittings at the Fermi surface that match the calculated altermagnetic band structure, and they show the splittings and associated energy gaps weaken and close when the sample is heated above the 178 K Néel temperature. If correct, the compound adds a cleavable, layered platform for studying altermagnetism at relatively high temperature.","feed_headline":"Altermagnetic spin splitting seen in layered Co1/4TaSe2","feed_subtitle":"ARPES and DFT tie momentum-split bands to antiferromagnetic order at 178 K.","key_machinery":"The central object is altermagnetic spin splitting: a momentum-dependent splitting of electronic bands into opposite spin channels that occurs even though the material has no net magnetization, here realized in a type A antiferromagnetic order with cobalt moments aligned ferromagnetically within each layer and antiparallel between layers. The identification rests on matching ARPES spectra to DFT band-structure calculations for that magnetic state, and on temperature-dependent ARPES showing the splitting and gaps close as the Néel temperature is crossed, tying the electronic signature to the magnetic order.","core_discovery":"The central claim is that Co1/4TaSe2 orders as a type A antiferromagnet at 178 K and that its electronic bands exhibit altermagnetic spin splitting: energy bands near the Fermi level are split into opposite-spin branches whose spin character is locked to momentum in a way that reverses between oppositely magnetized sublattices. The paper argues that the ARPES-measured band structure agrees with DFT calculations for this magnetic ground state, that the observed splitting is present below the Néel temperature and disappears above it, and that the temperature-driven band shifts and gap closure track the suppression of the altermagnetic order. The conclusion is that Co1/4TaSe2 represents a working layered altermagnet with spin splitting observable in photoemission.","pith_inferences":["A direct spin-resolved ARPES measurement, not reported in the paper, would confirm the opposite spin polarization of the split branches and rule out a nonmagnetic or spin-orbit explanation.","Other intercalated transition metal dichalcogenides with similar cobalt ordering might show the same phenomenon; the paper's temperature-dependent signature (band-gap closure near TN) gives a cheap screening method to search for them.","The claim implies that the altermagnetic order, not just the split band structure, controls the electronic reconstruction; this could be tested by measuring the same bands under applied strain that modifies the interlayer exchange."],"forward_implications":["Co1/4TaSe2 becomes one of the few layered compounds with reported altermagnetic spin splitting, and the cleavable structure makes it accessible to surface-sensitive probes.","Heating through 178 K should switch off the spin splitting, giving a temperature handle on spin-polarized electronic states without a net magnetization.","The reported band-structure agreement supports the DFT magnetic ground state as the correct starting point for modeling altermagnetic order in this family.","If the assignment holds, the compound offers a testbed for altermagnet-based spintronic proposals that require spin-polarized currents from an antiferromagnet."],"supporting_citations":[],"fun_headline_variants":["Layered altermagnet Co1/4TaSe2 shows spin-split bands","Co1/4TaSe2: first layered altermagnet with photoemission evidence","Spin splitting seen in altermagnet Co1/4TaSe2 at 178 K","ARPES confirms altermagnetic spin splitting in Co1/4TaSe2","Type A altermagnet Co1/4TaSe2: spin-split bands below 178 K"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The interpretation depends on the assumption that the actual magnetic order of Co1/4TaSe2 is the type A antiferromagnetic structure computed by DFT, with no other mechanism such as spin-orbit coupling or surface reconstruction producing the observed band splitting and its temperature dependence.","fun_headline_variants_meta":{"raw":{"variants":["Layered altermagnet Co1/4TaSe2 shows spin-split bands","Co1/4TaSe2: first layered altermagnet with photoemission evidence","Spin splitting seen in altermagnet Co1/4TaSe2 at 178 K","ARPES confirms altermagnetic spin splitting in Co1/4TaSe2","Type A altermagnet Co1/4TaSe2: spin-split bands below 178 K"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.0009,"raw_usage":{"total_tokens":3844,"prompt_tokens":886,"completion_tokens":2958,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":502,"completion_tokens_details":{"reasoning_tokens":2842}},"tokens_in":502,"tokens_out":2958,"duration_ms":19843,"temperature":1.0,"reasoning_tokens":2842,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T17:15:49.418810+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the spin polarization of the split Fermi-surface sheets with spin-resolved ARPES: altermagnetism requires the two sheets to carry opposite spin polarization that reverses across the antiferromagnetic sublattices. Alternatively, neutron diffraction that finds a different magnetic propagation vector, or observation that the splitting persists well above 178 K, would disprove the claim.","supporting_citations":[],"review_version":2}