{"id":"3f3735ad-91f7-450e-9884-bbfa089e5ad4","arxiv_id":"2507.04693","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":10,"one_line_summary":"LuOs3B2 is a 4.75 K type-II superconductor with strong correlations and an imaginary phonon mode, while YCo3B2 lacks superconductivity, and both show kagome band features.","lead":"This paper compares two kagome metals, LuOs3B2 and YCo3B2, confirming superconductivity in LuOs3B2 with Tc = 4.75 K and finding enhanced electron correlations and a phonon instability in it. The study maps how kagome-derived electronic features and correlations vary across a materials family, which is useful for designing correlated kagome superconductors.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Phonon-driven lattice-instability claim for LuOs3B2 is computed without spin-orbit coupling, despite SOC being dominant in this 5d compound; if the L-point imaginary mode is an SOC artifact, the central coexistence claim collapses.","rationale":"The reader's conditional verdict is reasonable, but I identify a different weakest link. The impurity-phase concern is real and explicitly acknowledged, yet the 4.75 K superconducting transition is supported by resistivity, magnetization, and a heat-capacity anomaly, and the known impurity phases (Os, LuOs2) do not provide an obvious alternative source of this Tc. The more load-bearing and less protected element of the central claim is the lattice instability, which underpins the proposed connection between correlations and charge-order tendencies. That instability rests entirely on phonon calculations performed without spin-orbit coupling for a 5d system where the paper itself shows SOC is significant. The same phonon calculation yields λ ≈ 1.96, in direct tension with the McMillan-derived λ ≈ 0.54, suggesting the low-frequency phonon sector—exactly where the imaginary modes and large λ live—is not quantitatively reliable. A SOC-inclusive phonon calculation is a decisive, concrete check: it directly tests whether the predicted instability is physical or an artifact. My recommendation remains CONDITIONAL, so the verdict is unchanged, but the condition should explicitly require this calculation rather than focusing only on impurity corrections.","tokens_in":14254,"tokens_out":10447,"duration_ms":123955,"concrete_test":"Recompute the phonon dispersion and α²F(ω) for LuOs3B2 with fully relativistic (SOC-inclusive) pseudopotentials on the same 3×3×6 q-grid, and relax a supercell containing the L-point distortion. If the imaginary mode at L remains with a real energy gain of order a few meV per formula unit, the instability claim is supported; if the mode hardens or the distortion collapses, the claim should be withdrawn or weakened.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's central predictive claim—that LuOs3B2 sits near a lattice instability and is a candidate for pressure/doping studies toward charge order—rests on imaginary phonon modes at Γ, A, and L, obtained from density-functional perturbation theory with scalar-relativistic pseudopotentials and no spin-orbit coupling (Methods section). This is the same compound for which the paper itself emphasizes that SOC strongly modifies the electronic structure. For 5d Os states, SOC can renormalize soft phonon branches, and the L-point mode singled out after dismissing the Γ modes as numerical artifacts has not been shown to survive a fully relativistic calculation. The concern is reinforced by two internal inconsistencies: the text reports a DFT electron-phonon coupling λ ≈ 1.96 for LuOs3B2, whereas the McMillan inversion from the measured Tc gives λ ≈ 0.54, and the abstract claims the calculations are 'consistent' with the observed Tc; and the predicted distorted structure is only referred to as 'not shown', while no CDW or structural transition is observed experimentally. If the L-point imaginary mode is an artifact of the scalar-relativistic approximation, the proposed coexistence of strong correlations and phonon instability is not established, and the paper reduces to a characterization study of a moderately correlated superconductor.","agreement_with_reader":"disagree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports an experimental and first-principles study of two kagome metals, LuOs3B2 and YCo3B2.  The experiments show that LuOs3B2 is a bulk type-II superconductor with Tc ≈ 4.75 K, evidenced by resistivity, magnetization, and heat capacity, and that YCo3B2 does not superconduct above 1.8 K.  From the measured susceptibility, resistivity, and heat capacity, the authors derive Wilson and Kadowaki-Woods ratios and conclude that both compounds are electronically correlated.  The DFT calculations describe the band structure, Fermi surface, and phonon spectra.  The phonon calculations for LuOs3B2 produce imaginary modes at Γ, A, and L, which the authors interpret as a lattice instability and use as a basis for proposing pressure or doping studies toward charge order.","tokens_in":14590,"tokens_out":6753,"duration_ms":68946,"significance":"If the central claims are established, the paper identifies a kagome metal in which strong electronic correlations and a phonon instability coexist, which would be an interesting target for future pressure and doping studies.  The experimental measurements are standard and appear to support bulk superconductivity in LuOs3B2.  The paper also makes falsifiable predictions, such as the lattice-instability tendency, and its description of the kagome-derived electronic structure is a useful contribution.  However, the theoretical pillar currently has an unresolved internal inconsistency and a missing spin-orbit-coupling check, so the significance is conditional: the coexistence claim is not yet firmly supported by the evidence as presented.","major_comments":[{"comment":"The imaginary modes at Γ, A, and L are computed with density-functional perturbation theory using scalar-relativistic norm-conserving pseudopotentials without spin-orbit coupling, although the paper itself emphasizes that SOC has the most significant effect on the band structure of LuOs3B2.  Since the L-point mode is the sole basis for the structural-instability and charge-order-candidacy claim, an SOC-inclusive phonon calculation or an explicit relaxation of the distorted structure with SOC is needed to show that the mode survives.  As it stands, the calculation does not exclude the possibility that the L-point instability is an artifact of the scalar-relativistic approximation.","section":"Methods; Phonon Calculations"},{"comment":"There is an unresolved quantitative inconsistency in the electron-phonon coupling.  From the measured Tc the authors obtain λep = 0.54 for μ* = 0.10 and 0.64 for μ* = 0.15, while the DFPT result is λe−ph = 1.96 for LuOs3B2.  The text states that the first-principles estimates are consistent with the observed Tc and that Tc ≈ 6 K is obtained in fair agreement, but with λ = 1.96 and the stated μ* range the McMillan formula would predict a substantially higher Tc for any reasonable ωlog; reproducing 6 K would require an unusually small ωlog, which is not reported.  The paper should present the Eliashberg function, the value of ωlog, and the μ* used for the 6 K estimate, and should reconcile the DFPT λ value with the McMillan-inverted value.","section":"Physical Properties (McMillan inversion); Phonon Calculations"},{"comment":"The LuOs3B2 sample contains approximately 5% LuOs2 and 4% Os impurity phases, and the authors state that these impurities prevented a good Rietveld refinement.  The measured susceptibility, resistivity, and heat capacity are then used without impurity subtraction to infer χP, γ, A, and hence the Wilson ratio ≈ 3 and Kadowaki-Woods ratio ≈ 48.  These ratios are central to the claimed electronic correlations, so the authors should quantify possible impurity contributions or compare with the single-phase samples reported in ref. [51] to demonstrate that the derived correlation parameters are intrinsic to LuOs3B2.","section":"Structure"}],"minor_comments":[{"comment":"The abstract and summary mention Fermi surface calculations revealing quasi-one-dimensional behavior along the c-axis in YCo3B2, but no Fermi surface results are presented in the Results section.  Either add the corresponding figure and discussion or remove this claim.","section":"Abstract; Results"},{"comment":"The text says intermediate-frequency modes are due to Co or Rh atoms, but the compounds studied contain Co and Os, not Rh.  This appears to be a typographical error.","section":"Phonon Calculations"},{"comment":"The suggestion of multi-gap superconductivity is based only on a reduced normalized heat-capacity jump.  A reduced jump can arise from strong coupling, anisotropy, or other effects, so the wording should be more cautious unless a two-gap analysis is provided.","section":"Fig. 5(b)"},{"comment":"The Fig. 1 caption refers to 'results of refinement' while the main text says a good Rietveld refinement was not possible and no refinement parameters are used.  The caption and text should be made consistent.","section":"Fig. 1 caption; Structure"},{"comment":"There are several typographical errors, including 'seperated', 'feild', and 'super-cell'; these should be corrected in a revision.","section":"Text"}],"recommendation":"major_revision","confidential_remarks":null},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Dear colleague,\n\nThe paper is worth knowing about as a data point in the RT3B2 kagome family, but the big claim—coexistence of strong correlations and a lattice instability in LuOs3B2—doesn't hold together as cleanly as the abstract suggests.\n\nWhat's genuinely new is the YCo3B2 characterization: resistivity, heat capacity, Kadowaki-Woods ratio ≈ 13, and the comparison to LuOs3B2. The experimental measurements are standard and look credible. Tc ≈ 4.75 K for LuOs3B2 with a heat capacity anomaly is consistent with the concurrent PRB work, and the authors honestly flag that in a note added. The kagome-derived electronic features (flat bands, Dirac cones, van Hove singularities) are clearly identified in the DFT.\n\nThe soft spots are real. First, the electron-phonon coupling: from McMillan inversion on the measured Tc they get λ ≈ 0.54–0.64, but their DFPT calculation gives λ = 1.96. They use both without saying how they fit together. That needs an explanation—either one of the estimates is wrong, or the McMillan formula is being pushed outside its range. Second, the phonon calculations are done scalar-relativistic, no SOC. For a 5d Os compound where they themselves stress that SOC strongly changes the band structure, the imaginary modes at Γ, A, L cannot be taken at face value. The L-point mode is the basis for the lattice-instability claim, and it may not survive a fully relativistic treatment. The predicted distorted structure is 'not shown,' and no CDW/structural transition is observed, so the instability claim is currently speculation. Third, the ~9% impurity phases (LuOs2, Os) could nudge the Wilson ratio and KWR; probably not enough to kill the correlation story, but they should estimate the effect. The 'tuning' in the title is also a bit strong for a two-sample comparison.\n\nOverall, the experimental core is functional and the correlation enhancement is likely real. The lattice-instability claim is the weak link. A serious referee should send this back for revision, asking for a resolution of the λ discrepancy, a fully relativistic phonon calculation or a clear caveat, and a quantitative assessment of the impurities. The paper is not a desk reject, but it's not ready as it stands.","headline":"Credible characterization of two kagome metals, but the coexistence claim is undermined by an unexplained electron-phonon coupling discrepancy and phonon calculations that omit spin-orbit coupling in a 5d compound.","tokens_in":15174,"tokens_out":6097,"would_cite":false,"duration_ms":67408,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["74.70.Ad","71.27.+a"],"model":"deepseek-v4-flash","headline":"The kagome metal LuOs3B2 is a bulk type-II superconductor at $T_c = 4.75$ K with enhanced correlations and imaginary phonon modes, while YCo3B2 is its correlated but non-superconducting counterpart.","keywords":["kagome lattice","LuOs3B2","YCo3B2","superconductivity","electronic correlations","Wilson ratio","Kadowaki-Woods ratio","phonon instability"],"falsifier":"A single-crystal or phase-pure sample of LuOs3B2 measured for susceptibility, resistivity, and heat capacity would settle the central claim: if $T_c = 4.75$ K, Wilson ratio ≈ 3, Kadowaki-Woods ratio ≈ 48, and the heat-capacity jump survive in the clean sample, the correlations are intrinsic; if the ratios shrink or the transition weakens, the reported impurity phases were carrying part of the signal.","tokens_in":14042,"feed_emoji":"⚛️","tokens_out":10319,"duration_ms":101786,"temperature":0.7,"pith_summary":"This paper tries to establish that the kagome metal LuOs3B2 is a bulk type-II superconductor at $T_c = 4.75$ K with sizable electronic correlations (Wilson ratio ≈ 3, Kadowaki-Woods ratio ≈ 48) and phonon spectra that contain imaginary modes, indicating a latent lattice instability. The companion compound YCo3B2 is presented as a non-superconducting counterpart with enhanced correlations (Kadowaki-Woods ratio ≈ 13) but no phonon instability. If true, the work places LuOs3B2 near a tipping point where strong correlations and a structural or charge-density-wave-like instability coexist, making it a concrete candidate for pressure or doping studies. A sympathetic reader would care because this is one of the few kagome metals where flat-band fermiology, correlation signatures, and phonon softening appear in the same material.","feed_headline":"LuOs3B2 is a correlated kagome superconductor with unstable phonons","feed_subtitle":"With Tc = 4.75 K, Wilson ratio ≈ 3, and imaginary phonon modes, pressure or doping could unlock charge order.","key_machinery":"The central object is the perfect kagome lattice of Os (or Co) atoms in the RT3B2 structure, which supplies the quasi-flat bands, Dirac cones, and van Hove singularities near the Fermi level. The argument is carried by three tools: the Wilson ratio and Kadowaki-Woods ratio, which convert measured susceptibility, specific heat, and resistivity into correlation-strength indicators; density functional theory plus density functional perturbation theory, which produce the band structures, Fermi surfaces, and phonon dispersions; and the McMillan formula, which translates the calculated electron-phonon coupling into a predicted superconducting $T_c$. The imaginary phonon modes at high-symmetry points, especially L, are the load-bearing signal connecting correlations to a possible charge-order or structural transition.","core_discovery":"On the paper's own terms: LuOs3B2 superconducts in bulk at $T_c = 4.75$ K, with magnetization, resistivity, and heat capacity all showing the transition, and the normalized heat-capacity jump is smaller than the single-gap BCS expectation, hinting at multigap behavior. First-principles calculations give an electron-phonon coupling λ ≈ 1.96 and a predicted $T_c ≈ 6$ K, in fair agreement with experiment, and the measured Wilson and Kadowaki-Woods ratios (≈3 and ≈48) indicate non-negligible correlations. Its calculated phonon spectrum has imaginary modes, notably at the L point, which the authors interpret as susceptibility to a structural distortion or charge-density-wave-like order. YCo3B2, by contrast, shows kagome flat bands, Dirac cones, and van Hove singularities, a Kadowaki-Woods ratio ≈13, no superconductivity above 1.8 K, and no imaginary phonon modes. The pair is offered as evidence that in this family the strength of electronic correlations and the tendency toward lattice instability can be tuned by switching the transition-metal site while preserving the kagome geometry.","pith_inferences":["An implication the authors leave implicit is that single-crystal or phase-pure samples of LuOs3B2 are needed to confirm the correlation estimates, because the ~5% LuOs2 and ~4% Os impurities could contribute to susceptibility, resistivity, or heat capacity.","A concrete extension would be hydrostatic pressure: if the L-point imaginary mode controls a real instability, pressure should drive LuOs3B2 toward a structural or charge-density-wave transition.","The quasi-linear $H_{c2}(T)$ behavior suggests the single-band WHH picture may be incomplete, so a two-band or strong-coupling analysis is a direct next test of the superconducting state."],"forward_implications":["LuOs3B2 becomes a concrete candidate for pressure or doping experiments aimed at driving the L-point phonon instability into a charge-density-wave or structural transition.","The smaller-than-BCS heat-capacity jump and the unusual quasi-linear upper-critical-field curve point to multigap or strong-coupling superconductivity, which spectroscopic gap measurements could test directly.","In YCo3B2, doping that moves the Fermi level down into the large density of states just below it could activate superconductivity or other correlation effects.","The contrast with LaRh3B2 (no strong correlations, no imaginary modes) and LuOs3B2 (both present) tightens the proposed link between electronic correlations and phonon anomalies in the RT3B2 family."],"supporting_citations":[{"why":"Supplies the initial report of RT3B2 superconductivity and the lattice parameters against which LuOs3B2 is compared.","marker":"[18]"},{"why":"Provides earlier transition-temperature values for this family that the measured 4.75 K transition is checked against.","marker":"[21]"},{"why":"Documents similar enhanced Wilson ratios in the kagome superconductor LaRu3Si2, the comparison that makes LuOs3B2 correlations look non-negligible.","marker":"[24]"},{"why":"The authors' earlier LaRh3B2 study supplies the kagome band features and the correlation-free, phonon-stable baseline for the family.","marker":"[29]"},{"why":"Defines the Kadowaki-Woods ratio used to quantify electronic correlations from the resistivity coefficient A and the specific-heat coefficient gamma.","marker":"[47]"},{"why":"Provides the Werthamer-Helfand-Hohenberg and Ginzburg-Landau expressions used to extract upper critical field, coherence length, and penetration depth.","marker":"[48]"},{"why":"Gives the McMillan formula used to translate electron-phonon coupling into a predicted superconducting critical temperature.","marker":"[49]"},{"why":"The concurrent independent report on LuOs3B2 with which the authors compare their superconducting and electronic-structure results, including the disagreement on single-phase synthesis.","marker":"[51]"}],"fun_headline_variants":["Kagome metals: swap Co for Os to turn on superconductivity and correlations","LuOs3B2: a correlated kagome superconductor with imaginary phonons","Tuning electronic correlations in kagome metals via transition-metal choice","Kagome metal LuOs3B2: Tc=4.75 K and imaginary phonons","Co-to-Os switch tunes kagome correlations, superconductivity, and phonons"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The paper's key assumption is that the measured superconductivity and correlation ratios come from LuOs3B2 itself, even though the sample contains about 5% of a different compound (LuOs2) and 4% osmium metal, and these impurities prevented a full structural refinement; if those phases contribute to the susceptibility, resistivity, or heat capacity, the correlation numbers and the bulk nature of the superconducting transition could be misattributed.","fun_headline_variants_meta":{"raw":{"variants":["Kagome metals: swap Co for Os to turn on superconductivity and correlations","LuOs3B2: a correlated kagome superconductor with imaginary phonons","Tuning electronic correlations in kagome metals via transition-metal choice","Kagome metal LuOs3B2: Tc=4.75 K and imaginary phonons","Co-to-Os switch tunes kagome correlations, superconductivity, and phonons"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001238,"raw_usage":{"total_tokens":5154,"prompt_tokens":1088,"completion_tokens":4066,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":704,"completion_tokens_details":{"reasoning_tokens":3958}},"tokens_in":704,"tokens_out":4066,"duration_ms":30890,"temperature":1.0,"reasoning_tokens":3958,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T19:42:33.767033+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A single-crystal or phase-pure sample of LuOs3B2 measured for susceptibility, resistivity, and heat capacity would settle the central claim: if $T_c = 4.75$ K, Wilson ratio ≈ 3, Kadowaki-Woods ratio ≈ 48, and the heat-capacity jump survive in the clean sample, the correlations are intrinsic; if the ratios shrink or the transition weakens, the reported impurity phases were carrying part of the signal.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the initial report of RT3B2 superconductivity and the lattice parameters against which LuOs3B2 is compared."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides earlier transition-temperature values for this family that the measured 4.75 K transition is checked against."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Documents similar enhanced Wilson ratios in the kagome superconductor LaRu3Si2, the comparison that makes LuOs3B2 correlations look non-negligible."},{"cited_title":"Chaudhary, Shama, J","cited_arxiv_id":null,"evidence_quote":"The authors' earlier LaRh3B2 study supplies the kagome band features and the correlation-free, phonon-stable baseline for the family."},{"cited_title":"Kadowaki and S","cited_arxiv_id":null,"evidence_quote":"Defines the Kadowaki-Woods ratio used to quantify electronic correlations from the resistivity coefficient A and the specific-heat coefficient gamma."},{"cited_title":"Singh, C","cited_arxiv_id":null,"evidence_quote":"Provides the Werthamer-Helfand-Hohenberg and Ginzburg-Landau expressions used to extract upper critical field, coherence length, and penetration depth."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"The concurrent independent report on LuOs3B2 with which the authors compare their superconducting and electronic-structure results, including the disagreement on single-phase synthesis."}],"review_version":1}