{"id":"59626c67-231f-4329-9349-0798cc7c9619","arxiv_id":"2607.16689","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"Muon-spin and specific-heat data on ScIr2−xSix are best described by a two-gap (s+d)-wave superconducting state, and ScIr2 transforms into a chiral R32 structure at TS≈190 K.","lead":"ScIr2 and its silicon-doped variant are shown to be unconventional superconductors with two gaps, one of them having nodes, and the parent compound switches to a chiral crystal structure at about 190 K. The paper combines muon-spin measurements, X-ray diffraction, thermodynamics and band calculations to position this kagome material as a rare platform for the interplay of flat bands, chirality and superconductivity.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The (s+d)-wave conclusion rests on specific-heat data borrowed from Ref. [51] for a sample whose Si content is only asserted to be 'comparable'; the muSR data alone do not favor (s+d).","rationale":"The reader identified the sample-composition matching and phonon-subtraction assumptions as the weakest point. I agree, and the quantitative detail strengthens the concern: the muSR data alone are either neutral or slightly favor (s+s) over (s+d), so the entire unconventional-pairing conclusion hinges on external specific-heat data. This is not an internal contradiction or a statement outside consensus; it is a question of whether the decisive dataset belongs to the same material. The paper itself flags the matching issue in the Figure 4 caption, so this is a genuine limitation, not a manufactured one. A direct re-measurement of Ce/T on the muSR samples would settle it. Because the concern is addressable and the muSR and structural results remain valuable, the verdict should stay CONDITIONAL rather than moving to ACCEPT or REJECT. The reader's reasoning is sound; no verdict adjustment is needed.","tokens_in":24236,"tokens_out":3348,"duration_ms":35935,"concrete_test":"Measure zero-field specific heat on the exact same physical samples used for the muSR experiments (ScIr2 and ScIr1.82Si0.18), subtract phonons with the same C/T = γn + βT² + δT⁴ procedure, and redo the two-gap (s+s) and (s+d) fits on the same temperature range. If the re-measured Ce/T data do not reject (s+s) with a comparable χ² margin to Table 1, then the unconventional (s+d) pairing claim loses its decisive support. Optionally, determine the actual Si content of the Ref. [51] specific-heat sample by EDX or SXRD refinement and check whether it matches ScIr1.82Si0.18.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim—two-gap (s+d) pairing with one nodal gap—is decided almost entirely by the specific-heat reanalysis, not by the new muSR data. Table 1 shows that TF-µSR alone does not discriminate: for ScIr2, χ²_r is 4.4 for (s+s) versus 5.4 for (s+d); for ScIr1.82Si0.18, it is 3.1 versus 2.4. The decisive discrimination comes from Ce/T: (s+s) gives χ²_r >20 while (s+d) gives 3.1 and 2.64. Those Ce/T data were not measured in this work; they are taken from Ref. [51]. The paper's Figure 4 caption states that 'comparable Si concentrations are expected' between the Ref. [51] samples and the muSR samples, and that prior extra phases also lowered the actual Si content. This is an assertion, not a demonstration. If the specific-heat sample has a different actual x, Tc, γn, or phonon background, then the combined fit—with w, Δ1, and Δ2 ostensibly constrained by the muSR superfluid-density fits—is fitting a different superconductor. The derived d-wave weight could then be a fitting artifact rather than a property of ScIr2−xSix. The phonon subtraction C/T = γn + βT² + δT⁴ is also fragile, especially for ScIr1.82Si0.18, where β = 0.20(3) mJ/mol-K⁴ is very small and may absorb electronic contributions. This is the least-secure load-bearing condition of the paper's strongest claim.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This manuscript reports a combined muon-spin spectroscopy (μSR), single-crystal X-ray diffraction (SXRD), electrical transport, magnetization, and density-functional-theory study of the kagome superconductors ScIr2 and ScIr1.82Si0.18. The authors claim that ScIr2 undergoes a cubic-to-rhombohedral (R32) structural transition near 190 K that produces a chiral Ir chain, and that both compounds exhibit unconventional superconductivity described by a two-gap (s+d)-wave model in which one gap is nodal. The pairing-symmetry assignment is based on fits of six gap models to the temperature-dependent superfluid density inferred from transverse-field μSR and to zero-field electronic specific-heat data taken from the authors' earlier work (Ref. [51]). Zero-field μSR shows preserved time-reversal symmetry, which is used to exclude chiral (s+p) pairing.","tokens_in":24655,"tokens_out":6476,"duration_ms":64183,"significance":"If the central claim holds, the paper identifies a rare kagome superconductor with structural chirality and unconventional, partially nodal pairing, making ScIr2–xSix a valuable platform for studying the interplay of flat bands, correlations, topology, and superconductivity. The manuscript contributes new experimental data of good quality: TF- and ZF-μSR measurements, SXRD identification of the R32 phase, and DFT band structures showing flat bands near the Fermi level. These are significant assets. However, the (s+d) pairing conclusion is not established by the new μSR data alone; it is decided by a reanalysis of specific-heat data from a previous paper. The significance is therefore contingent on resolving the sample-matching and phonon-subtraction issues identified below.","major_comments":[{"comment":"The assignment of (s+d) pairing is not determined by the new μSR data. In Table 1, the reduced χ² for (s+s) versus (s+d) from the superfluid-density fits are 4.4 vs 5.4 for ScIr2 and 3.1 vs 2.4 for ScIr1.82Si0.18; for ScIr2 the (s+s) model is actually slightly better. The decisive discrimination (χ²_r >20 vs 3.1/2.64) comes entirely from the Ce/T fits using zero-field data from Ref. [51]. The Figure 4 caption only asserts that 'comparable Si concentrations are expected' and relabels the Ref. [51] sample ScIr1.75Si0.25 as ScIr1.82Si0.18; the actual Si content of that specific-heat sample is not measured. The phonon subtraction C/T = γn + βT² + δT⁴ is also fragile: for ScIr1.82Si0.18, β = 0.20(3) mJ/mol·K⁴ is very small and could absorb low-temperature electronic contributions, biasing Ce/T in the region T/Tc < 0.3 where (s+s) and (s+d) differ. Please either measure Ce/T on the same sample","section":"§2.4 / Table 1 / Fig. 4"},{"comment":"The text in §2.4 states that in the two-gap Ce/T fit 'w, Δ1, and Δ2' are 'the same parameters as for the superfluid-density fits'. However, Table 1 lists different numerical values for the μSR and Ce/T fits; for example, for ScIr2 with the (s+d) model, w = 0.8 for μSR but 0.63 for Ce/T, and Δ1 = 0.27 meV for μSR but 0.39 meV for Ce/T. Please clarify whether the Ce/T fits were constrained to the μSR-derived parameters or were fitted independently. If they were fitted independently, the claim of a single consistent two-gap model is weaker; if they were constrained, Table 1 and the fits must be corrected. As written, this inconsistency prevents the reader from judging the actual degree of constraint in the combined analysis.","section":"§2.4 / Table 1"},{"comment":"The authors correctly state in §2.3 that 'TF-μSR measurements in a higher magnetic field can distinguish between these two cases', citing CuIr2Te4 as an example. This discriminating experiment is not performed in the present work, and the (s+d) conclusion instead relies on the borrowed Ce/T data. Given that the new μSR data alone do not select (s+d), the conclusion of unconventional superconductivity would be considerably strengthened by carrying out the acknowledged high-field μSR experiment on the same samples, or by explicitly tempering the concluding claim until such data are available.","section":"§2.3 / §4"}],"minor_comments":[{"comment":"Typo: 'bewteen' should read 'between'.\n","section":"Experimental Section"},{"comment":"Typo: 'analogus' should read 'analogous'.\n","section":"Fig. 6 caption"},{"comment":"The sentence 'the extra phases observed in previous studies also resulted in lower actual Si concentrations' is unclear; please rephrase to state explicitly how the composition of the Ref. [51] sample was inferred.\n","section":"Fig. 4 caption"},{"comment":"The notation in Eq. (3) — the Fermi-surface average, the integration variable ε, and the angular dependence gk — is not fully specified. Please define the average ⟨...⟩_FS and the relation between ε and k explicitly.\n","section":"Eq. (3)"},{"comment":"The table headings 'Δ0^{μSR} (meV), w' and 'Δ0^{Ce/T} (meV), w' are ambiguous. Separate columns for Δ1, Δ2 and w would improve readability and avoid confusion between the two fits.\n","section":"Table 1"}],"recommendation":"major_revision","confidential_remarks":"The paper contains high-quality μSR and structural data, but the headline physics claim — unconventional (s+d) pairing with a nodal gap — is currently decided by a reanalysis of specific-heat data from Ref. [51], not by the new measurements. The muSR data alone are nearly degenerate between (s+s) and (s+d), and the specific-heat sample's actual Si content is only asserted to be comparable. The parameter inconsistency between the μSR and Ce/T fits in Table 1 is an additional concern that should be fixed in revision. If the authors can supply specific-heat measurements on the same batches used for muSR, or otherwise robustly establish sample equivalence and phonon subtraction, the paper could become a strong contribution."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Quick take: this is a competent muSR plus single-crystal XRD study. The genuinely new results are the structural transition in ScIr2 to a chiral R32 phase at ~190 K, confirmed by SXRD with a clear refinement contrast, and the TF/ZF-muSR characterization showing preserved time-reversal symmetry and a two-gap superfluid density. The paper is worth a serious referee, but the headline pairing conclusion—two-gap (s+d) with one nodal gap—is less secure than the writing suggests.\n\nWhat it does well: the SXRD refinement distinguishing R32 from Fd-3m at 80 K is convincing (chi2 of 1.02 vs 19.7). The ZF-muSR spectra are clean and the absence of TRS breaking is solid. The superfluid-density analysis is standard, and the data alone clearly rule out single-gap d- and p-wave models. The band-structure calculations are reasonable support for multiband physics and flat bands near EF.\n\nThe soft spot is exactly where you pointed. Table 1 shows that TF-muSR alone hardly differentiates (s+s) from (s+d): reduced chi2 values are 4.4 vs 5.4 for ScIr2 and 3.1 vs 2.4 for the doped sample. The decisive discrimination comes from Ce/T, where (s+s) gives chi2 >20 and (s+d) gives about 3. Those specific-heat data were not measured in this work; they are taken from the authors' previous paper, Ref. [51]. The Figure 4 caption states only that the samples have \"comparable Si concentrations\" because the same preparation method was used. That is an assertion, not a demonstration. If the actual Si content differs, or if the phonon subtraction C/T = gamma_n + beta T^2 + delta T^4 is inadequate—and beta for ScIr1.82Si0.18 is only 0.20(3) mJ/mol-K^4, small enough to absorb electronic contributions—the inferred d-wave weight could be a fitting artifact. The authors themselves acknowledge that higher-field muSR is the test that could distinguish the two models, but they do not perform it.\n\nI want to be fair: none of this invalidates the structural result or the unconventional character in a broad sense. The paper is honest about the model-selection logic, and the claim is conditional rather than absurd. But the phrase \"solid evidence\" in the conclusion overreaches. The central argument holds up only if the sample-matching assumption is accepted, and that is the load-bearing assumption to flag.\n\nWho gets value: the kagome-superconductor and noncentrosymmetric-superconductor communities. I would not cite it in my own near-term work, but I would bring it to a reading group focused on muSR-based pairing determinations.\n\nRecommendation: send to peer review. Ask the authors to either provide higher-field muSR data, demonstrate the Si-content match between the two sample batches with a direct measurement, or soften the conclusion to \"consistent with (s+d) rather than (s+s).\"","headline":"New muSR and SXRD data make ScIr2-xSix a plausible chiral kagome superconductor, but the nodal (s+d) claim rests on borrowed specific heat, not the new muSR.","tokens_in":25202,"tokens_out":1978,"would_cite":false,"duration_ms":21602,"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":"Muon-spin and specific-heat data pin ScIr2−xSix as a two-gap (s+d)-wave superconductor, with one gap containing line nodes.","keywords":["kagome lattice","unconventional superconductivity","two-gap superconductivity","muon spin rotation","specific heat","chiral crystal","flat bands","ScIr2"],"falsifier":"Measure the zero-field electronic specific heat on the exact same ScIr2 and ScIr1.82Si0.18 batches used for the muon-spin experiments, then re-run the two-gap fits: if the low-temperature Ce/T data are fully reproduced by a nodeless (s+s)-wave model with the same fitted parameters, the nodal d-wave component would disappear. Alternatively, repeat transverse-field muon-spin rotation at a substantially higher applied field (e.g., 100 mT rather than 30 mT), where the s-gap is suppressed and the nodal d-component should become more visible in the temperature dependence of the superfluid density.","tokens_in":24052,"feed_emoji":"🌀","tokens_out":3279,"duration_ms":37731,"temperature":0.7,"pith_summary":"This paper reports that ScIr2−xSix, a family of kagome-lattice superconductors, hosts unconventional superconductivity: its low-energy excitations cannot be explained by a single fully gapped order parameter. Combining muon-spin rotation and specific-heat analyses, the authors argue that both the parent ScIr2 and the Si-doped ScIr1.82Si0.18 are described by a two-gap (s+d)-wave model in which one gap is nodeless and the other has line nodes. The paper also establishes that ScIr2 undergoes a cubic-to-rhombohedral structural transition near 190 K, so its low-temperature phase contains a slightly distorted Ir kagome layer and an Ir chiral chain, making it a topological chiral crystal. The significance is that this is a rare kagome system where flat bands near the Fermi level, strong correlations, structural chirality, and unconventional superconductivity coexist, offering a platform to study their interplay.","feed_headline":"Two-gap (s+d) pairing found in kagome superconductor ScIr2","feed_subtitle":"Muon-spin and specific-heat data show one gap with nodes, making ScIr2−xSix a rare chiral kagome unconventional superconductor.","key_machinery":"The central object is the two-gap 'alpha model' for the superconducting state: both the superfluid density ρsc(T) and the electronic specific heat Ce(T)/T are written as weighted sums of two independent gap contributions, with the same weight w, maximum gaps Δ1 and Δ2, and angular gap functions gk = 1 (s-wave) or gk = cos2φ (d-wave) used in both fits. Carrying the argument is the combination of this model with transverse-field muon-spin data for the penetration depth and with zero-field muon-spin data showing preserved time-reversal symmetry; the latter eliminates the point-node (s+p) option, leaving (s+d) as the preferred two-gap description. Band-structure calculations supply the multiband","core_discovery":"The central claim is that the superconducting pairing in ScIr2−xSix is unconventional and multigap. The temperature-dependent superfluid density, measured by transverse-field muon-spin rotation, and the zero-field electronic specific heat can both be accurately fitted by a two-gap (s+d)-wave model: an isotropic s-wave gap plus a d-wave gap whose cos2φ angular dependence produces line nodes. The d-wave weight is about 20%, so the nodeless component dominates, which explains why the low-temperature superfluid density is only weakly temperature-dependent. Time-reversal symmetry is preserved in the superconducting state, ruling out the tested (s+p)-wave and chiral p-wave options. Band-structure","pith_inferences":["If the (s+d) assignment is correct, a clear testable prediction is that increasing the applied magnetic field in transverse-field muon-spin experiments should suppress the s-wave gap more strongly than the d-wave gap, making the nodal signature more prominent in the superfluid density; conversely, if that does not happen, an anisotropic but nodeless single-gap fit may be the more economical descri","The two-dome superconducting phase diagram in Si content could be reinterpreted as a structural effect: in the first dome the material is rhombohedral with a reduced density of states from antisymmetric spin-orbit splitting, while in the second dome it is cubic with flat bands closer to the Fermi level; this suggests that flat-band-based DOS arguments taken from the cubic structure alone may be mi","The paper's own caveat about 'comparable Si concentrations' between the muon-spin samples and the reference specific-heat samples implies an unstated fragility: a direct measurement of specific heat on the identical batches used for muon-spin would settle whether the claimed d-wave component is real or an artifact of sample mismatch.","Given the preserved time-reversal symmetry in the bulk, the most interesting extension is the surface state: a chiral crystal with strong spin-orbit coupling could harbor topological or chiral surface superconductivity even when the bulk is a TRS-preserving s+d superconductor, and surface-sensitive probes such as scanning tunneling microscopy or Kerr rotation would be the natural test."],"forward_implications":["ScIr2−xSix is an unconventional, multigap superconductor, so any single-gap fully gapped description is inadequate for its low-energy thermodynamics and superfluid response.","Because time-reversal symmetry is preserved, chiral p-wave or (s+p)-wave pairing is excluded in the bulk; the data point to a nodeless-plus-nodal combination, i.e., an (s+d)-type state.","The multiband electronic structure, with multiple Fermi-surface sheets and flat bands near the Fermi level, means the pairing likely arises from a mix of electron-phonon coupling on some bands and spin/charge-fluctuation-mediated pairing on the flat-band-dominated band.","ScIr2 is a noncentrosymmetric chiral crystal at low temperature, making it a candidate for mixed-parity pairing and for exotic surface superconductivity, even if the bulk state preserves time-reversal symmetry.","The (Ca,Sr,Ba,Zr,Th)Ir2 sister compounds, with tunable spin-orbit coupling, become natural next targets for testing how SOC strength affects the nodal gap structure and the pairing symmetry."],"fun_headline_variants":["Unconventional s+d superconductivity in chiral kagome ScIr2","Multigap nodal superconductivity in chiral kagome ScIr2Si","Kagome superconductor ScIr2Si shows two-gap nodal pairing","Chiral kagome ScIr2 hosts unconventional nodal superconductivity","Evidence for two-gap s+d pairing in kagome superconductor ScIr2"],"cache_read_input_tokens":2304,"weakest_assumption_plain":"The discrimination between (s+d) and (s+s) pairing relies on the zero-field specific-heat data from a separate study being taken on samples with essentially the same actual silicon content as the muon-spin samples, and on the phonon background being adequately captured by a simple γn+βT2+δT4 subtraction; if either fails, the inferred d-wave weight could be an artifact of the fit.","fun_headline_variants_meta":{"raw":{"variants":["Unconventional s+d superconductivity in chiral kagome ScIr2","Multigap nodal superconductivity in chiral kagome ScIr2Si","Kagome superconductor ScIr2Si shows two-gap nodal pairing","Chiral kagome ScIr2 hosts unconventional nodal superconductivity","Evidence for two-gap s+d pairing in kagome superconductor ScIr2"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000386,"raw_usage":{"total_tokens":1920,"prompt_tokens":835,"completion_tokens":1085,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":579,"completion_tokens_details":{"reasoning_tokens":997}},"tokens_in":579,"tokens_out":1085,"duration_ms":7462,"temperature":1.0,"reasoning_tokens":997,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-01T20:13:49.874122+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the zero-field electronic specific heat on the exact same ScIr2 and ScIr1.82Si0.18 batches used for the muon-spin experiments, then re-run the two-gap fits: if the low-temperature Ce/T data are fully reproduced by a nodeless (s+s)-wave model with the same fitted parameters, the nodal d-wave component would disappear. Alternatively, repeat transverse-field muon-spin rotation at a substantially higher applied field (e.g., 100 mT rather than 30 mT), where the s-gap is suppressed and the nodal d-component should become more visible in the temperature dependence of the superfluid density.","supporting_citations":[],"review_version":1}