{"id":"0752a7f7-08ad-483d-ab5f-125ff45bf1ed","arxiv_id":"2507.18373","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":5,"one_line_summary":"In samarium-based infinite-layer nickelates, the measured exchange coupling is about 20% smaller than in praseodymium-based nickelates despite a nearly two-fold higher Tc, opposite to the trend in cuprates.","lead":"Using x-ray scattering, researchers measured magnetic ripples in a new family of high-temperature superconducting nickelates based on samarium. They found the magnetic interaction is about 20% weaker than in a related nickelate even though the superconducting temperature is roughly twice as high, a result that challenges a simple cuprate-like relationship.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The claimed ~20% smaller J1 in SECS vs PSNO is only ~1.3σ with the quoted errors, and cross-beamline systematics are uncontrolled, so the central cuprate-contrast claim is not yet established.","rationale":"The reader's weakest_assumption focuses on the validity of the spin-wave model and the single-magnon nature of the low-energy mode. That is a legitimate interpretive concern, but I see a more immediate load-bearing problem: the headline comparison is not statistically significant. Given J1 = 46.6 ± 4.9 and J1 = 57.3 ± 7.1 meV, the difference is 10.7 ± 8.6 meV, only about 1.24σ. Furthermore, SECS and PSNO data were collected at different beamlines with different resolutions, temperatures, and sample configurations, with no reported cross-calibration or systematic-error analysis. This means the central conclusion — a reduced exchange coupling despite higher Tc, opposite to the cuprate trend — could be an artifact of noise or beamline-dependent fitting biases. The paper's positive contributions, including the first RIXS observation of dispersive paramagnons in superconducting Sm-based infinite-layer nickelates and the doping-dependent softening, are solid and do not depend on the comparative claim. The reader's CONDITIONAL verdict is appropriate: a joint statistical analysis and/or a cross-beamline control would be the natural condition to meet. If such an analysis shows ΔJ > 2σ robustly, the paper's claim would be substantially strengthened; if not, the authors should present the result as no significant reduction rather than as a 20% decrease. I therefore keep the verdict unchanged.","tokens_in":12487,"tokens_out":5064,"duration_ms":59753,"concrete_test":"Perform a joint profile-likelihood re-analysis of the SECS and PSNO paramagnon pole energies: fit both dispersions simultaneously with the Heisenberg J1–J2 model, allowing independent J1 and J2 per compound, and compute the confidence interval on ΔJ = J1_PSNO − J1_SECS. Repeat the fit with (i) J2 fixed to zero, (ii) Zc varied over 1.0–1.3, (iii) peak energies ωmax instead of pole energies ω0, and (iv) a beamline-resolution offset term in the DHO convolution to mimic the 67 vs 46 meV difference. If the 95% interval for ΔJ excludes zero in all variants, the ~20% reduction is robust; if any variant yields ΔJ < 2σ, the central cuprate-contrast claim is not established and the conclusion should be softened to a null or upper-limit comparison.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The load-bearing quantitative claim is the comparison J1(SECS) = 46.6 ± 4.9 meV versus J1(PSNO) = 57.3 ± 7.1 meV, presented as a ~20% reduction that contrasts with the cuprate Tc–J correlation. The difference is 10.7 meV; the quadrature error is sqrt(4.9^2 + 7.1^2) = 8.6 meV, giving ΔJ/σ ≈ 1.24, corresponding to a two-sided p-value of about 0.21. At conventional significance, the data do not establish a reduction. The quoted uncertainties are only per-fit statistical errors, and the two compounds were measured on different beamlines (TPS 41A vs Diamond I21) with different energy resolutions (67 vs 46 meV), different temperatures (30 vs 16 K), and different film/substrate/cap configurations. No cross-calibration, shared reference sample, or systematic-error budget is reported. A resolution difference alone can bias fitted DHO pole positions for broad damped modes by an amount comparable to the claimed 10.7 meV difference. Even accepting the single-magnon linear-spin-wave interpretation with Zc = 1.187, the data as presented do not support the central claim. The additional model concern — undoped S = 1/2 spin-wave theory applied at p ≈ 0.19 — mainly affects whether fitted J1 values are intrinsic exchange couplings, but the more immediate weakness is that the comparison itself is not statistically significant.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports Ni L-edge resonant inelastic x-ray scattering (RIXS) measurements on superconducting Sm-based infinite-layer nickelate thin films (SECS), including an optimally doped sample with Tc,onset ~35 K and an overdoped sample, and compares them with optimally doped Pr-based PSNO films. Dispersive paramagnon modes are observed in both SECS doping levels and in PSNO. Fitting the extracted dispersion with a J1-J2 linear spin-wave model yields J1 = 46.6 ± 4.9 meV and J2 = -2.4 ± 3.7 meV for OP SECS, and J1 = 57.3 ± 7.1 meV and J2 = -1.6 ± 5.2 meV for OP PSNO. The authors interpret the roughly 20% smaller effective exchange coupling in SECS, despite its higher Tc, as contrasting with the positive Tc-exchange correlation in hole-doped cuprates, and suggest that additional factors such as multi-band effects and rare-earth hybridization control Tc in the nickelates.","tokens_in":12826,"tokens_out":4658,"duration_ms":51317,"significance":"If the central comparison is correct, the paper reports a notable result: the highest-Tc infinite-layer nickelate would have a smaller in-plane exchange coupling than a lower-Tc Pr-based counterpart, inverting the cuprate-like Tc-J correlation. This would sharpen the case that spin fluctuations alone do not set the Tc scale in these nickelates and would motivate further work on rare-earth 5d hybridization and three-dimensionality. The raw data also provide a useful new measurement of paramagnons in the Sm-based family. However, the key quantitative claim currently rests on a difference that is only about 1.2 standard deviations given the quoted errors, and the two compounds were measured at different beamlines with different resolutions, temperatures, and sample environments, with no explicit systematic-error budget. The significance of the paper therefore depends on whether the statistical and systematic basis of the J1 comparison can be strengthened.","major_comments":[{"comment":"The central claim of a ~20% reduction in J1 is based on J1(SECS) = 46.6 ± 4.9 meV versus J1(PSNO) = 57.3 ± 7.1 meV. The difference is 10.7 meV, while the quadrature uncertainty is sqrt(4.9^2 + 7.1^2) = 8.6 meV, giving a significance of about 1.2 sigma (two-sided p ~ 0.21). By standard statistical criteria, these data do not establish a reduction, let alone a quantitative 20% value. Because the abstract and discussion present this comparison as the main finding, the authors should either provide substantially smaller or better-justified uncertainties, a joint fit that directly tests the difference, or explicitly reframe the claim as a tentative trend.","section":"Discussion and Fig. 3e"},{"comment":"The SECS and PSNO data were collected on different beamlines with different energy resolutions (67 meV at TPS 41A versus 46 meV at Diamond I21), at different sample temperatures (30 K versus 16 K), with different scattering geometries, and on different film/substrate/cap stacks. The authors state that the 'beamline-specific photon energy offset has not been considered.' No cross-calibration or shared reference sample is reported. For broad damped modes, a resolution difference of this size can bias fitted damped-harmonic-oscillator pole positions by an amount comparable to the claimed 10.7 meV difference. The authors should provide a systematic uncertainty estimate or demonstrate, for example through a resolution-matching analysis, that the SECS-versus-PSNO comparison is robust to these experimental differences.","section":"Methods: RIXS experiments"},{"comment":"The exchange couplings are extracted by applying an undoped S = 1/2 linear spin-wave model with a fixed quantum renormalization factor Zc = 1.187 to OP SECS at nominal doping p = 0.19. At this doping the magnon is already strongly damped and softened by hole doping, as the paper itself acknowledges when interpreting the reduced effective couplings. The fitted J1 and J2 are therefore effective parameters whose relation to intrinsic exchange constants is model-dependent. If the low-energy RIXS mode contains significant multi-magnon or charge spectral weight, or if the undoped spin-wave description is quantitatively inappropriate at p = 0.19, the 20% comparison between SECS and PSNO may not be meaningful. The manuscript should at least discuss the sensitivity of J1 to the choice of Zc and to potential multi-magnon contributions.","section":"Discussion and Eq. (1)"}],"minor_comments":[{"comment":"The caption for panel (b) uses 'PNSO' instead of 'PSNO'; this typo should be corrected.","section":"Fig. 2 caption"},{"comment":"The text contains 'nickealtes' instead of 'nickelates' in the sentence discussing charge order; this should be corrected.","section":"Introduction"},{"comment":"Since the SECS and PSNO data were taken at 30 K and 16 K, respectively, a brief statement on whether temperature renormalization of the paramagnon could affect the comparison would be helpful.","section":"Methods: RIXS experiments"},{"comment":"The data availability statement only offers data 'on a reasonable request'; for a quantitative claim of this nature, deposition in a public repository would improve reproducibility.","section":"Data availability"}],"recommendation":"major_revision","confidential_remarks":"The paper addresses a timely and important question, and the raw RIXS data on the Sm-based nickelate family are valuable. The main issue is evidentiary: the headline comparison is not statistically significant under the quoted errors and is further complicated by cross-beamline systematics. This is a correctable problem, either through additional experiments with a common reference sample or through a revised, more cautious framing of the central claim. I see no indication of circular reasoning or other integrity concerns."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The genuinely new piece here is the first RIXS study of superconducting Sm-based infinite-layer nickelates (SECS). The paramagnon dispersions are clean, the overdoped comparison is a nice touch, and the paper is honest about the doping dilution and the theoretical prediction (ref. 35) that J should be smaller in SmNiO2. The qualitative observation—robust ~100 meV spin excitations persist in SECS despite Tc near 35 K—is a real addition to the nickelate RIXS program. Credit where due: the data handling, the DHO fitting, and the inclusion of both OP and OD samples are all done carefully. I believe the RIXS spectra themselves.\n\nThe soft spot is the central quantitative claim. J1(SECS) = 46.6 ± 4.9 vs J1(PSNO) = 57.3 ± 7.1 meV: the quoted errors make the difference about 1.2 sigma, which does not establish a 20% reduction. On top of that, the two compounds were measured at different beamlines (TPS 41A vs Diamond I21), with different energy resolutions (67 vs 46 meV), different temperatures, and different film configurations. No cross-calibration or systematic-error budget is reported. A resolution mismatch alone can shift fitted DHO poles for broad damped modes by an amount on the order of the claimed 10 meV. The authors do flag the beamline-specific offset in the Methods, which is good, but they don't quantify what it does to the comparison.\n\nI don't think the single-magnon linear-spin-wave model at p ≈ 0.19 is fatal—it's the standard approach in this field and the overdoped data soften as expected, so the mode assignment is reasonable. The statistical weakness of the headline comparison is the real issue. The direction of the effect agrees with theory, which helps, but the paper should not present a ~1.2-sigma difference as a demonstrated cuprate-contrasting trend. That needs a combined fit, a shared reference sample, or at least a systematic-error estimate.\n\nFor whom is this paper? Nickelate specialists and RIXS practitioners. It deserves a serious referee—the first Sm-based nickelate RIXS data merit careful review even if the central claim needs revision. I would take it for review, but I'd push hard for a reanalysis of the SECS/PSNO comparison and a toned-down abstract.","headline":"First RIXS look at Sm-based infinite-layer nickelates; the data are solid and useful, but the headline Tc-versus-J comparison rests on a ~1.2-sigma difference and uncontrolled cross-beamline systematics.","tokens_in":13490,"tokens_out":632,"would_cite":true,"duration_ms":8656,"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":"The paper reports that in Sm-based infinite-layer nickelates, the effective exchange coupling is about 20% smaller than in Pr-based compounds even though Tc is twice as high, opposite to the cuprate trend.","keywords":["infinite-layer nickelates","RIXS","paramagnon","exchange coupling","superconductivity","SmNiO2","spin fluctuations","Tc enhancement"],"falsifier":"A phase-pure undoped SmNiO2 would allow a model-independent check: if its magnon bandwidth is not close to 100 meV, then the small $J_1$ in SECS is a doping-induced softening rather than a property of the Sm-based rare earth, and the comparison with PSNO would no longer support the paper's conclusion.","tokens_in":12295,"feed_emoji":"🧲","tokens_out":6037,"duration_ms":54957,"temperature":0.7,"pith_summary":"This paper asks what determines the high superconducting transition temperature in the new Sm-based infinite-layer nickelate (SECS). Using resonant inelastic x-ray scattering, the authors observe paramagnons—spin excitations—in both optimally and overdoped SECS and measure their dispersion. Fitting the dispersion with a spin-wave model, they find the nearest-neighbor exchange coupling is about 20% weaker in SECS than in the Pr-based compound PSNO, even though SECS superconducts at a much higher temperature. That is the opposite of the cuprate correlation between magnetic coupling and Tc, pointing to other ingredients—such as three-dimensionality or rare-earth hybridization—as important for pairing.","feed_headline":"Weaker magnetic coupling, higher Tc in Sm nickelates","feed_subtitle":"RIXS shows Sm-based nickelates have ~20% less exchange coupling than Pr-based, yet Tc about four times higher.","key_machinery":"The core object is the paramagnon, a damped collective spin excitation of the nickelate planes, measured by Ni $L$-edge RIXS. Its momentum-dependent pole energy is fit to a linear spin-wave dispersion for a doped $S=1/2$ square lattice with nearest- ($J_1$) and next-nearest-neighbor ($J_2$) exchange, rescaling magnon energies by a quantum renormalization factor $Z_c = 1.187$. This converts the measured bandwidth and zone-boundary curvature into exchange couplings, enabling the comparison between SECS and PSNO.","core_discovery":"The paper claims that the effective nearest-neighbour exchange coupling in optimally doped Sm-based infinite-layer nickelate (SECS) is $J_1 = 46.6 \\pm 4.9$ meV, about 20% smaller than in Pr-based PSNO ($J_1 = 57.3 \\pm 7.1$ meV), while the superconducting onset temperature is roughly four times higher (35 K vs 9 K). This inverted relation between magnetic coupling and $T_c$ is the opposite of what is seen in hole-doped cuprates and implies that in-plane spin fluctuations alone do not set the $T_c$ scale in nickelates.","pith_inferences":["The 20% contrast is based on comparing two different rare-earth hosts at slightly different lattice constants and doping; a systematic series across rare-earth elements with identical doping would test whether the trend is monotonic in ionic radius.","If the effective coupling reduction comes from added three-dimensionality, one might expect an out-of-plane exchange $J_\\perp$ to appear; measuring the $c$-axis dispersion of the paramagnon (if any) would directly confirm the proposed mechanism.","The interpretation hinges on the validity of a single-magnon model at 19% doping; an alternative doped-spin-wave treatment might shift both $J_1$ values but the relative ordering is likely robust, strengthening the qualitative conclusion."],"forward_implications":["If the exchange coupling is genuinely weaker while $T_c$ is higher, in-plane spin fluctuations alone cannot set the $T_c$ scale in infinite-layer nickelates.","The persistence of a large exchange coupling (~47 meV) in a superconductor with $T_c \\sim 35$ K keeps spin-fluctuation-mediated pairing viable, but its strength is not the limiting factor.","The observed doping softening of the paramagnon in overdoped SECS resembles cuprate behavior, suggesting a common evolution of spin correlations with hole doping.","A cuprate-like design rule—maximize in-plane magnetic coupling to maximize $T_c$—does not transfer to nickelates; other parameters, such as interlayer coupling or rare-earth 5$d$ hybridization, must be tuned instead."],"supporting_citations":[{"why":"RIXS study of Nd-based infinite-layer nickelate establishing the paramagnon dispersion and exchange couplings used as a baseline.","marker":"[7]"},{"why":"First-principles calculation predicting ~20% smaller in-plane exchange in SmNiO2 than in Nd/La/Pr, which the data confirm.","marker":"[35]"},{"why":"Growth and characterization of the SECS films with Tc,onset ~35 K, the sample set for this RIXS study.","marker":"[36]"},{"why":"Growth and superconductivity of the PSNO film (Tc,onset ~9 K) used as the direct comparison.","marker":"[39]"},{"why":"The linear spin-wave model and quantum renormalization factor Zc=1.187 used to extract J1 and J2 from the paramagnon dispersion.","marker":"[49]"},{"why":"Cuprate study showing positive correlation between Tc and paramagnon energy, providing the contrast case.","marker":"[56]"},{"why":"Earlier RIXS of other infinite-layer nickelates showing similar spin excitations and softening, supporting a consistent description.","marker":"[33]"}],"fun_headline_variants":["Nickelates invert cuprate trend: weaker spins, higher Tc","Sm nickelates show lower spin coupling yet over 4x Tc","RIXS: Sm-based nickelates couple spins less, superconduct more","Weaker magnetic exchange, record Tc in Sm nickelates"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The central inference rests on assuming that the RIXS peak is a single paramagnon describable by a linear spin-wave model with a fixed renormalization factor even at 19% hole doping; if the mode includes multi-magnon or charge contributions, the fitted $J_1$ values are not true exchange couplings.","fun_headline_variants_meta":{"raw":{"variants":["Nickelates invert cuprate trend: weaker spins, higher Tc","Sm nickelates show lower spin coupling yet over 4x Tc","RIXS: Sm-based nickelates couple spins less, superconduct more","Weaker magnetic exchange, record Tc in Sm nickelates"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000213,"raw_usage":{"total_tokens":1390,"prompt_tokens":882,"completion_tokens":508,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":498,"completion_tokens_details":{"reasoning_tokens":434}},"tokens_in":498,"tokens_out":508,"duration_ms":5405,"temperature":1.0,"reasoning_tokens":434,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T14:33:41.958960+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A phase-pure undoped SmNiO2 would allow a model-independent check: if its magnon bandwidth is not close to 100 meV, then the small $J_1$ in SECS is a doping-induced softening rather than a property of the Sm-based rare earth, and the comparison with PSNO would no longer support the paper's conclusion.","supporting_citations":[{"cited_title":"Lu , author M","cited_arxiv_id":null,"evidence_quote":"RIXS study of Nd-based infinite-layer nickelate establishing the paramagnon dispersion and exchange couplings used as a baseline."},{"cited_title":"Zhang , author J","cited_arxiv_id":null,"evidence_quote":"First-principles calculation predicting ~20% smaller in-plane exchange in SmNiO2 than in Nd/La/Pr, which the data confirm."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Growth and characterization of the SECS films with Tc,onset ~35 K, the sample set for this RIXS study."},{"cited_title":"Ren , author J","cited_arxiv_id":null,"evidence_quote":"Growth and superconductivity of the PSNO film (Tc,onset ~9 K) used as the direct comparison."},{"cited_title":"Rossi , author H","cited_arxiv_id":null,"evidence_quote":"Earlier RIXS of other infinite-layer nickelates showing similar spin excitations and softening, supporting a consistent description."}],"review_version":1}