{"id":"dc46dcf2-3bd0-4bc0-8032-a08c83151150","arxiv_id":"2506.16165","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"Biaxial tensile strain of 1.50% on RbV3Sb5 enhances its superconducting transition temperature by about 75% and shifts its upper critical field anisotropy toward a more two-dimensional response.","lead":"Applying a large tensile stretch to the kagome superconductor RbV3Sb5 raises its superconducting temperature from 0.82 K to 1.46 K and makes the superconductivity behave more like a two-dimensional system. The result shows that strain can tune both the critical temperature and the dimensional character of this material, which may help clarify how superconductivity works in the kagome family.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Strain calibration is the load-bearing point: the 1.50% biaxial strain and the quantitative ΔTc/Tc curve rest on calculated thermal-mismatch strain transfer, not on a measured lattice strain of the RbV3Sb5 crystal; if transfer is incomplete or inhomogeneous, the headline enhancement must be…","rationale":"The reader's weakest assumption identifies the same load-bearing concern: the actual strain on RbV3Sb5 is not directly measured, and the paper's own Supplementary Material description calls it 'nominal strain.' This is more upstream than the dimensionality fit in Eq. (1): every strain label in Fig. 1(b) and Fig. 4(c) inherits the strain-calibration assumption, and the most novel quantitative numbers (1.50%, 75% enhancement) are directly hostage to it. The concern is not a disagreement with consensus or an attack on the authors; it is a missing direct measurement of a quantity the central claim explicitly depends on. I considered whether the angular-dependent Hc2 analysis and the α/β decomposition are the weakest point, since error bars are absent and the data span only ±10° around θ=0. That is a real secondary concern, but if the strain-axis calibration fails, the quantitative strain-Tc relationship and the comparison with CsV3Sb5 change even while the angular fits remain internally consistent. Conversely, if the strain calibration is verified by direct lattice measurement, the remaining concerns are about fit robustness and would not overturn the reported Tc enhancement. The verdict should remain CONDITIONAL, as the reader already stated; no movement is needed, and the concrete test would either retire the concern or require recalibration of the headline numbers.","tokens_in":12955,"tokens_out":6982,"duration_ms":80284,"concrete_test":"Perform low-temperature synchrotron micro-XRD (or micro-Laue) on the actual bonded RbV3Sb5/ZrW2O8 device used for the ε=1.50% measurement, mapping the lattice parameter across the crystal (e.g., 5–10 positions) at base temperature and comparing with the free-standing crystal and with the nominal ε=1.50% expectation. Also repeat for one intermediate device (e.g., sapphire). If the measured in-plane strain is significantly below nominal (e.g., <1.2%) or varies by more than ~0.2% across positions, the strain axis in Fig. 1(b) and the 1.50% headline must be recalibrated and the comparison with CsV3Sb5 revisited. If the measured strain matches nominal to within uncertainty and is homogeneous, the central quantitative claim is supported.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central quantitative claim—ε=1.50% on RbV3Sb5 raising Tc from 0.82 K to 1.46 K, and the ΔTc/Tc versus ε curve in Fig. 1(b)—treats the thermal-mismatch strain calculated for the substrate as the strain actually experienced by the 800×250×10 µm³ crystal. The manuscript says the strain is 'calculated as described in Ref. [13]' and justifies full transfer with 'the small size of the sample ensures that strain is effectively imposed'; the Supplementary Material itself is described as reporting 'nominal strain induced on RbV3Sb5 by substrates.' Strain gauges are mentioned, but they are on the substrate side of the bond; no measurement of the RbV3Sb5 lattice parameter under strain is reported, and no post-run inspection for microcracking or adhesive creep is described. If the adhesive partially relaxes, if the crystal fractures under 1.5% tensile strain, or if strain is inhomogeneous across the contact, then the strain axis of Fig. 1(b), the extracted ε_A1g comparison with CsV3Sb5, and the phrase 'strain ε=1.50%' all need correction. The qualitative ordering of tensile versus compressive Tc and the dimensional crossover direction would survive, but the quantitative 75% enhancement at a stated strain would not be established.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports biaxial strain tuning of the kagome metal RbV3Sb5 using thermal-expansion-mismatch substrates. The authors measure resistance transitions on crystals bonded to substrates with different thermal expansion coefficients, extracting a strain-dependent Tc that increases from about 0.83 K (free-standing) to 1.46 K on a ZrW2O8 substrate, which they associate with a calculated 1.50% tensile strain. They further measure Hc2(T) and Hc2(θ) for two tensile-strained samples, infer a multiband-to-single-band crossover between ε=1.15% and ε=1.50%, and use a combined Ginzburg-Landau/Tinkham model to argue that the superconducting dimensionality shifts toward two-dimensional behavior under tensile strain.","tokens_in":13290,"tokens_out":5014,"duration_ms":55499,"significance":"If the strain calibration is reliable, this work provides a simple and effective method for applying large biaxial tensile strain to layered kagome superconductors, and it reports a striking 75% Tc enhancement together with a dimensionality crossover. The use of ZrW2O8 as a negative-thermal-expansion substrate to reach 1.5% biaxial strain is a notable technical achievement, and the Hc2(θ) measurements with a vector magnet are a clear strength. The quantitative conclusions, however, rest on inferred rather than directly measured strain values and on fits whose statistical uncertainties are not reported.","major_comments":[{"comment":"The central quantitative claim—ε=1.50% tensile strain raising Tc from 0.82/0.83 K to 1.46 K, and the ΔTc/Tc versus ε curve in Fig. 1(b)—treats the thermal-mismatch strain calculated for the substrate as the strain actually experienced by the RbV3Sb5 crystal. The text states that the strain is 'calculated as described in Ref. [13]' and that 'the small size of the sample ensures that strain is effectively imposed,' but no direct measurement of the RbV3Sb5 lattice parameter under strain is reported. Strain gauges are mentioned, yet they are on the substrate side, and no post-run inspection for microcracking or adhesive creep is described. Please provide either a direct strain measurement (e.g., X-ray diffraction on the strained crystal) or a quantitative calibration/uncertainty analysis of the strain transfer, and address the possibility of partial relaxation or inhomogeneous strain.","section":"Sample preparation / Fig. 1"},{"comment":"No error bars or uncertainties are reported for Tc, Hc2, the anisotropy factor γ, or the fitting weights α and β. Given that Tc and Hc2 are defined by a 10% resistance criterion with finite transition widths, the stated 75% enhancement, the upturn in ΔTc/Tc beyond ε=0.84%, and the differences in γ and α between strains cannot be assessed for statistical significance. Please add uncertainties derived from transition widths, repeated measurements, or fitting procedures, and propagate them into the derived quantities.","section":"Figures 1(b), 3, and 4(c)"},{"comment":"The multiband-to-single-band crossover rests on a 'trace of an upturn' near t=1 for H//ab at ε=1.15% (Fig. 3(c)), but no quantitative analysis of this feature is provided. The WHH simulation with α=0 and λ=0 is shown only for ε=1.50% (Fig. 3(d)), not for ε=1.15%. Please fit both datasets with the same model, define an objective criterion for the upturn (e.g., deviation from a WHH curve), and specify the temperature range over which it is observed. Without this, the claim of a crossover from multi-band to single-band behavior is not quantitatively supported.","section":"Fig. 3(c) and multiband interpretation"},{"comment":"The WHH simulation fixes the Maki parameter α=0 and spin-orbit coupling λ=0 without justification for RbV3Sb5. The extracted orbital-limited fields H_orb^{c2}(0)=0.37 T (H//ab) and 0.03 T (H//c) depend directly on these assumptions. Please discuss the validity of neglecting spin-orbit and paramagnetic effects for this material and show the sensitivity of the extracted H_orb^{c2}(0) values to finite α and λ.","section":"WHH simulation, Fig. 3(d)"},{"comment":"The combined GL/Tinkham model in Eq. (1) is used to quantify the 2D/3D character through α and β, and the text states that α+β=1 is 'confirmed,' but no fit uncertainties, goodness-of-fit metrics, or full angular range used in the fits are reported. Figure 4(a)-(b) shows data only within about ±10°–20° of θ=0°, where the GL and Tinkham models differ most in curvature but where the discrimination may also be sensitive to small systematic errors in Hc2(0°). Please report the full angular range, the fit residuals, and the uncertainties in α and β, and clarify whether the model is intended as a phenomenological interpolation or has a derived basis.","section":"Eq. (1) and Fig. 4"}],"minor_comments":[{"comment":"The free-standing Tc is stated as 0.82 K in the abstract and 0.83 K in the main text and Fig. 1(a); please make these consistent.","section":"Abstract / main text"},{"comment":"The sentence 'they are found to be found to be 0.37 T and 0.03 T' contains a duplicated phrase; please correct.","section":"Section on Hc2 results"},{"comment":"The statement that 'the strain of sample and that of substrate were characterized by strain gauges' is ambiguous, because strain gauges cannot easily be attached to a 10 µm-thick crystal; please clarify the gauge placement and what quantity was actually measured.","section":"Sample preparation"},{"comment":"The caption describes 'the solid line represents the simulated Hc2(θ) by Tinkham model while the dash gray line represents the simulated Hc2(θ) by Ginzburg-Landau anisotropic mass model,' whereas the text refers to 'dotted line' and 'solid line'; please align the terminology.","section":"Fig. 4 caption and text"},{"comment":"References [49–52] provide examples of the combined model but not a derivation; if such a derivation exists, please cite it or else state explicitly that Eq. (1) is a phenomenological interpolation.","section":"Eq. (1) references"}],"recommendation":"major_revision","confidential_remarks":"The strain-calibration issue is the main risk to the central claim. If the authors can supply a direct strain measurement or a convincing transfer-efficiency calibration, the paper could become acceptable. The lack of error bars throughout is also a concern for a letter-style report, as several qualitative conclusions (upturn, multiband-to-single-band crossover, α changes) may hinge on small effects. The reviewer did not have access to the Supplementary Material, which is referenced for strain details and the ε_A1g extraction; this should be provided in the revision."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague,\n\nQuick take on arXiv:2506.16165. The paper reports Tc enhancement in RbV3Sb5 under biaxial tensile strain, from ~0.82 K to 1.46 K at a nominal 1.50% strain, using thermal-mismatch substrates. That's new for this compound, and the data look internally consistent: Tc rises monotonically with tensile strain, Hc2 anisotropy grows, and the angular dependence shifts toward the Tinkham 2D limit. The comparison with the biaxial component of uniaxial strain on CsV3Sb5 is a thoughtful way to place the result, and the authors are appropriately careful in attributing the likely tuning parameter to c-axis strain via the Poisson effect.\n\nThe soft spot is exactly where the stress-test note points: the strain axis is calculated, not measured. Strain gauges are on the substrate, and the authors argue the small sample ensures full transfer, but there is no direct lattice strain measurement on the RbV3Sb5 crystal and no post-run check for cracking or adhesive relaxation. So the quantitative 1.50% and the 75% enhancement carry an unquantified systematic uncertainty. The qualitative ordering—tensile raises Tc, compressive lowers it—would survive even if transfer is incomplete, and the dimensional crossover direction is robust. But the exact shape of the ΔTc/Tc versus ε curve, including the claimed upturn, rests on nominal strains. To their credit, the Supplementary Material apparently labels the strain as \"nominal,\" so this is not hidden.\n\nAlso, no error bars on Tc, Hc2, gamma, alpha, or beta, and no public data. For a letter that is common, but it matters here because several inferences (multi-band to single-band, alpha/beta weights) are based on small differences. The WHH fits with α=λ=0 are fine for extracting H_orb, but the \"single-band\" claim rests mainly on the disappearance of a small upturn, so I'd treat that as suggestive, not proven.\n\nOverall, the central observation is credible and worth taking seriously. The strain calibration concern is real but typical for this technique, and the authors are transparent about it. This deserves a serious referee; the main requests should be uncertainty estimates, a fuller description of the strain calibration, and ideally at least one direct check (XRD or micrograph of the strained crystal). I'd cite it if I worked on kagome superconductors or strain tuning.","headline":"Credible strain-tuning result on RbV3Sb5 with a real but standard caveat: the strain axis is calculated from thermal mismatch, not measured on the crystal, and the paper would benefit from uncertainty estimates and a direct strain check.","tokens_in":13925,"tokens_out":1770,"would_cite":true,"duration_ms":20169,"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":"Applying 1.50% biaxial tensile strain to RbV3Sb5 raises its superconducting transition temperature from 0.82 K to 1.46 K, a 75% enhancement, and shifts the superconductivity toward two-dimensional behavior.","keywords":["kagome metal","RbV3Sb5","biaxial strain","superconducting critical temperature","upper critical field","two-dimensional superconductivity","negative thermal expansion","strain tuning"],"falsifier":"Measure the lattice parameters of the strained RbV3Sb5 crystal directly at low temperature, for example by X-ray diffraction of the bonded device; if the actual strain is smaller than 1.50% or is inhomogeneous across the crystal, the reported strain-$T_c$ curve and the inferred two-dimensional crossover would need revision.","tokens_in":12771,"feed_emoji":"🧲","tokens_out":10225,"duration_ms":89759,"temperature":0.7,"pith_summary":"This paper reports that stretching the kagome metal RbV3Sb5 in the crystallographic plane by 1.50% raises its superconducting transition temperature from 0.82 K to 1.46 K, a 75% increase. The strain is applied by bonding thin crystals to substrates with different thermal expansion, using ZrW2O8, a negative thermal expansion material, to achieve the largest tension. The authors use upper critical field measurements as a function of temperature and field angle to argue that the enhanced superconducting state is qualitatively different: at 1.15% strain the field-temperature behavior is multi-band, while at 1.50% it becomes single-band, and the angular dependence shifts toward two-dimensional superconductivity. The results matter because they show that biaxial strain can tune not only $T_c$ but also the dimensionality of superconductivity in the kagome family, and they suggest c-axis compression as the controlling parameter.","feed_headline":"Stretching a kagome crystal 1.5% lifts its superconductivity 75%","feed_subtitle":"Biaxial tensile strain raises Tc of RbV3Sb5 from 0.82 K to 1.46 K and pushes it toward 2D superconductivity.","key_machinery":"The central object is the biaxial strain device: a thin RbV3Sb5 crystal glued to a substrate whose thermal expansion differs, so cooling imposes an in-plane strain calculated from the mismatch. The large tensile value $\\epsilon = 1.50\\%$ is reached with ZrW2O8, a negative thermal expansion material. To diagnose the superconducting state, the paper uses two fitting frameworks: the Werthamer-Helfand-Hohenberg (WHH) model for single-band $H_{c2}(T)$, and a combined anisotropic-mass Ginzburg-Landau/Tinkham model for $H_{c2}(\\theta)$, with weights $\\alpha$ (Tinkham, 2D-like cusp) and $\\beta$ (GL, 3D-like smooth) summing to 1. The shift in $\\alpha$ with strain is the quantitative measure of dimensionality change.","core_discovery":"The central discovery is that biaxial tensile strain of $\\epsilon = 1.50\\%$ on RbV3Sb5, produced by bonding the crystal to a ZrW2O8 substrate, raises $T_c$ from 0.82 K to 1.46 K, a 75% enhancement, while compressive strain lowers it to 0.61 K. The paper reports a roughly linear rise in $\\Delta T_c/T_c$ up to $\\epsilon \\approx 0.84\\%$, followed by an upturn at larger strain. Upper critical field data show an upturn near $T_c$ for $H \\parallel ab$ at $\\epsilon = 1.15\\%$, interpreted as multi-band superconductivity, which disappears at $\\epsilon = 1.50\\%$, leaving single-band behavior described by the WHH model. Angular dependence of $H_{c2}$ at 30 mK is fit with a combined Ginzburg-Landau/Tinkham model: the Tinkham weight $\\alpha$ increases from 0.30 in the free-standing crystal to 0.55 at 1.50% strain, and the anisotropy ratio $\\gamma = H_{c2}^{\\parallel ab}/H_{c2}^{\\parallel c}$ rises from 6.7 to 11.3, indicating a shift toward two-dimensional superconductivity. The authors conclude that the in-plane tensile strain, via the Poisson effect, compresses the $c$-axis and that this $c$-axis shortening is the main tuning parameter for $T_c$.","pith_inferences":["Editorial extension: If the abrupt upturn above $\\epsilon \\approx 0.84\\%$ comes from a Lifshitz transition that removes three-dimensional Fermi pockets, then CsV3Sb5 at comparable strains should show a similar kink, and angle-resolved quantum oscillations on strained samples would test this directly.","Editorial extension: The reported $\\alpha = 0.55$ still leaves substantial three-dimensional weight, so the paper establishes a trend toward, not a full realization of, two-dimensional superconductivity; whether larger strain yields $\\alpha \\to 1$ is an open test.","Editorial extension: Strain transfer is rarely perfect; if the true crystal strain is smaller than the nominal 1.50%, the intrinsic $T_c$ response to strain could be even steeper than shown, which would strengthen the c-axis-driven enhancement picture.","Editorial extension: Applying the same negative-thermal-expansion substrate method to KV3Sb5, the other low-$T_c$ member of the family, would test whether two-dimensional character and $T_c$ enhancement track together across the kagome metals."],"forward_implications":["Biaxial tensile strain can be used as a systematic tuning knob for RbV3Sb5, converting a low-$T_c$ member of the kagome family into a higher-$T_c$, more two-dimensional superconductor.","The nonlinear upturn in $\\Delta T_c/T_c$ beyond $\\epsilon \\approx 0.84\\%$ suggests that even larger tensile strain could raise $T_c$ further, and the same experiment on CsV3Sb5 may show a similar upturn at sufficient strain.","Identifying c-axis compression as the dominant tuning parameter connects the biaxial strain results to hydrostatic pressure experiments, where the c-axis also shrinks.","The strained-device platform permits angular $H_{c2}$ measurements and is compatible with quantum oscillation studies, so the normal-state Fermi surface can be probed in the same strained state."],"supporting_citations":[{"why":"supplies the self-flux growth method for the RbV3Sb5 single crystals used in every strained device.","marker":"[36]"},{"why":"gives the procedure for calculating the biaxial strain induced by substrate thermal mismatch, which assigns the reported epsilon values.","marker":"[13]"},{"why":"reports the negative thermal expansion of ZrW2O8, the substrate that produces the largest tensile strain of 1.50%.","marker":"[40]"},{"why":"provides the CsV3Sb5 uniaxial strain data used for the DeltaTc/Tc comparison and the argument that c-axis strain dominates.","marker":"[42]"},{"why":"documents the multi-band Hc2 upturn in CsV3Sb5 used as the interpretive baseline for the RbV3Sb5 data.","marker":"[46]"},{"why":"provides the WHH model used to simulate the single-band Hc2(T) at epsilon=1.50%.","marker":"[47]"},{"why":"provides the Tinkham model for 2D superconductivity used in the angular Hc2 fits.","marker":"[48]"},{"why":"introduces the combined Ginzburg-Landau/Tinkham fitting form (equation 1) that quantifies the 2D/3D weights alpha and beta.","marker":"[49]"}],"fun_headline_variants":["Biaxial strain lifts RbV3Sb5 Tc by 75%","75% superconductivity boost in RbV3Sb5 from biaxial strain","Kagome RbV3Sb5: 1.5% strain raises Tc 75%, moves toward 2D","Strain enhances RbV3Sb5 superconductivity 75% and dimensionality shift"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The results assume that the strain actually experienced by the RbV3Sb5 crystal equals the strain calculated from the substrate thermal expansion, with no relaxation, cracking, or adhesive slippage.","fun_headline_variants_meta":{"raw":{"variants":["Biaxial strain lifts RbV3Sb5 Tc by 75%","75% superconductivity boost in RbV3Sb5 from biaxial strain","Kagome RbV3Sb5: 1.5% strain raises Tc 75%, moves toward 2D","Strain enhances RbV3Sb5 superconductivity 75% and dimensionality shift"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001018,"raw_usage":{"total_tokens":4425,"prompt_tokens":1199,"completion_tokens":3226,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":815,"completion_tokens_details":{"reasoning_tokens":3134}},"tokens_in":815,"tokens_out":3226,"duration_ms":22361,"temperature":1.0,"reasoning_tokens":3134,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T23:44:03.747261+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the lattice parameters of the strained RbV3Sb5 crystal directly at low temperature, for example by X-ray diffraction of the bonded device; if the actual strain is smaller than 1.50% or is inhomogeneous across the crystal, the reported strain-$T_c$ curve and the inferred two-dimensional crossover would need revision.","supporting_citations":[{"cited_title":"Wang , author W","cited_arxiv_id":null,"evidence_quote":"supplies the self-flux growth method for the RbV3Sb5 single crystals used in every strained device."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"gives the procedure for calculating the biaxial strain induced by substrate thermal mismatch, which assigns the reported epsilon values."},{"cited_title":"Evans , author T","cited_arxiv_id":null,"evidence_quote":"reports the negative thermal expansion of ZrW2O8, the substrate that produces the largest tensile strain of 1.50%."},{"cited_title":"Qian , author M","cited_arxiv_id":null,"evidence_quote":"provides the CsV3Sb5 uniaxial strain data used for the DeltaTc/Tc comparison and the argument that c-axis strain dominates."},{"cited_title":"Ni , author S","cited_arxiv_id":null,"evidence_quote":"documents the multi-band Hc2 upturn in CsV3Sb5 used as the interpretive baseline for the RbV3Sb5 data."},{"cited_title":"Werthamer , author E","cited_arxiv_id":null,"evidence_quote":"provides the WHH model used to simulate the single-band Hc2(T) at epsilon=1.50%."},{"cited_title":"Tinkham ,\\ title title Effect of Fluxoid Quantization on Transitions of Superconducting Films , \\ @noop journal journal Phys","cited_arxiv_id":null,"evidence_quote":"provides the Tinkham model for 2D superconductivity used in the angular Hc2 fits."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"introduces the combined Ginzburg-Landau/Tinkham fitting form (equation 1) that quantifies the 2D/3D weights alpha and beta."}],"review_version":1}