{"id":"a38cf71a-e0e2-478d-8d11-2944d58a7dcc","arxiv_id":"2608.00512","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":1,"one_line_summary":"Fully ab initio SCDFT calculations predict spin-fluctuation-driven dx2-y2(±)-wave two-gap superconductivity in La, Pr, and Nd infinite-layer nickelates, with computed Tc matching experiment.","lead":"The paper predicts, from a first-principles superconductivity calculation, that strontium-doped infinite-layer nickelates superconduct with a d-wave, sign-changing gap driven by magnetic spin fluctuations, not lattice vibrations. The predicted transition temperatures match measured values near 9, 12 and 15 K for the La, Pr and Nd compounds.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Central SF-driven Tc claim hinges on unvalidated ALDA Stoner susceptibility: Eq. (3)'s Stoner enhancement is not quantified or benchmarked.","rationale":"The reader's weakest assumption already identified the ALDA spin susceptibility and the unspecified Sr-doping model. My independent reading of the manuscript confirms that the most load-bearing weakness is the unvalidated Stoner-enhanced susceptibility, because every quantitative statement about the pairing mechanism flows through Eq. (3) and the SCDFT kernel. The paper does contain genuine supporting evidence: the Fermi surface for LaSrNiO agrees with ARPES, the phonon dispersion matches earlier calculations, and the calculated quasiparticle DOS compares well with one STS spectrum near zero energy. These validate normal-state and quasiparticle aspects, but they do not constrain I χ0(q) near Q. Since the mechanism claim rests on the SF interaction being an order of magnitude larger than EPC and Coulomb repulsion, and since the reported Tc values ('agree well with experiments') could plausibly be tuned by the undocumented Stoner parameter, the concern is material. The proposed computational test—scanning I over a physically motivated range and watching Tc and the gap symmetry—would directly decide whether the mechanism is robust or an artifact of a single unvalidated input. I therefore keep the reader's CONDITIONAL verdict rather than escalating, because the issue is addressable and the paper's qualitative scenario is consistent with several experimental hints. No red flag of circular fitting or deliberate misrepresentation is present; the gap is in documentation and sensitivity analysis.","tokens_in":19079,"tokens_out":2891,"duration_ms":36219,"concrete_test":"Recompute Table II(c) with the same input data but with the Stoner parameter I varied over a physically plausible range (e.g., ±20% around the ALDA value, or using RPA with U = 2, 3, 4 eV on Ni 3d), and report Tc and the gap symmetry. If Tc changes by more than ~50% or the gap loses its dx2-y2(±) structure, the central claim is not robust to the magnetic-response input. Additionally, compare the computed χ(q) with available inelastic neutron scattering/RIXS data on infinite-layer nickelates; if no data exist, this benchmark should be flagged as missing.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's central conclusion—SF-driven dx2-y2(±) pairing with Tc ~7–16 K—rests on the magnitude of the SF interaction. In the simplified argument (Sec. VI, Eq. (3)), V_eff(k,k') = (3/4) I^2 χ0(q)/(1 - I χ0(q)). Because χ0(q) peaks near Q=(π/a,π/a), the denominator can strongly amplify even modest uncertainties in I or in the peak height of χ0. The paper reports no numerical value for I, no convergence data for the q/k grids used in the susceptibility, no actual comparison between ALDA and RPA results (only a sentence stating they 'do not differ significantly'), and no benchmark of χ(q) against inelastic neutron scattering or RIXS. ALDA is an adiabatic approximation for a strongly correlated Ni 3d shell; no Hubbard U or self-interaction correction is applied to the magnetic response. Since the same kernel enters the SCDFT gap equation (Eq. (1)) and the renormalization Z_SF, the quantitative claims—SF an order of magnitude stronger than EPC/Coulomb, Tc matching experiment, and sign-changing d-wave gap—all inherit this sensitivity. The Stoner parameter I is effectively an undocumented input; with only one free parameter reported, the agreement with experimental Tc is not independent evidence of the mechanism. The unspecified 20% Sr doping in a one-formula-unit cell is a secondary concern, but the magnetic-response kernel is the more load-bearing issue.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper presents fully ab initio SCDFT calculations of the superconducting state in optimally doped infinite-layer nickelates Re_0.8Sr_0.2NiO_2 (Re = La, Pr, Nd), treating electron-phonon coupling, screened Coulomb repulsion, and spin-fluctuation pairing on an equal footing. The central claims are that all three materials are two-band superconductors with sign-changing d_{x^2-y^2}(±) gaps of B1g symmetry, that the pairing is driven by antiferromagnetic spin fluctuations near q ≈ (π/a, π/a), and that the calculated Tc values (7.3, 12.7, 16.1 K) agree with experiment. The mechanism is supported by computer experiments in Sec. VI in which turning off the spin-fluctuation kernel reduces Tc to ~0.01 K, and by analysis of the Lindhard response function showing nesting peaks near the BZ corner. The paper also predicts STS spectra and compares the Fermi surface with ARPES for LaSrNiO.","tokens_in":19385,"tokens_out":2486,"duration_ms":37011,"significance":"If the central result holds, this is a significant contribution to the nickelate superconductivity debate: it provides a parameter-free, first-principles framework that identifies a magnetic pairing mechanism and a concrete d-wave gap structure, in contrast to previous GW-based phonon-mediated s-wave predictions (Ref. 31). The switch-off tests, self-consistent solution of the SCDFT gap equation, and agreement of the calculated Fermi surface with ARPES for LaSrNiO are genuine strengths. The predictions for STS spectra are falsifiable and should stimulate experiments. However, the quantitative SF strength and hence the magnitude of Tc and the relative dominance of μ_SF over λ and μ_ee depend on a spin susceptibility computed in ALDA for a strongly correlated Ni 3d shell, with an undocumented Stoner parameter I in Eq. (3). This caveat is load-bearing, not cosmetic.","major_comments":[{"comment":"The Stoner exchange parameter I in V_eff(k,k') = (3/4) I^2 χ_0(q)/(1 - I χ_0(q)) is never assigned a numerical value, and no derivation or DFT-based estimate is given. Because the RPA-like denominator strongly amplifies χ_0 near the nesting peaks, the resulting μ_SF, Tc, and the claimed order-of-magnitude dominance of SF over EPC/Coulomb all depend sensitively on I. The statement in Sec. II that RPA and ALDA results 'do not differ significantly' is not documented with any data, and no benchmark of χ_0(q) against RPA, RIXS, or neutron data is provided. The paper should report I, specify how it is obtained, and show the sensitivity of Tc and gap symmetry to I (and to the ALDA/RPA choice). Without this, the central quantitative claim is not fully established.","section":"Sec. VI, Eq. (3); Sec. II"},{"comment":"The calculations use a one-formula-unit cell for Re_0.8Sr_0.2NiO_2, but the text never states how the 20% Sr substitution is modeled (e.g., virtual crystal approximation, supercell, or rigid-band doping). The Fermi surface nesting that controls the Lindhard response peaks and the d-wave gap structure is sensitive to doping and to the position of the chemical potential. The alloying approximation should be described explicitly, and its effect on χ_0(q) and Tc should be assessed, at least for one representative compound.","section":"Sec. III; Sec. VI"},{"comment":"No convergence tests are reported for the BZ k/q grids, the tetrahedron integration, or the SCDFT gap-equation discretization. Since the susceptibility peaks in Figs. 5 and 6 are sharp and the SCDFT Tc values are obtained by extrapolation over a temperature mesh, convergence of Tc, Δ_max, and the gap structure should be demonstrated. This is particularly important because the SF kernel enters both the pairing kernel and the renormalization Z_SF, and small changes in the peak height of χ_0 can change Tc substantially.","section":"Secs. II, III, V"}],"minor_comments":[{"comment":"Typographical errors: 'National Center for Theoretical Science s' and 'Academia Sinic a' in the author affiliations.","section":"Affiliations"},{"comment":"The sentence 'Its unit cell contains one formula unit (f.u.)' should be reconciled with the disordered Re_0.8Sr_0.2 composition; the disorder model needs to be stated here.","section":"Sec. III"},{"comment":"The discussion of the GW-based s-wave prediction (Ref. 31) is fair, but the comparison would be strengthened by a brief discussion of the different Fermi surface topologies and doping treatments; currently the reader must infer them from the cited works.","section":"Sec. VII and Appendix B"},{"comment":"In the caption, 'Figs. 5(b) and 5(b)' should presumably read 'Figs. 5(b) and 5(d)'; similarly check references in Fig. 6 captions.","section":"Fig. 5 caption"},{"comment":"The Allen-Dynes McMillan formula is stated with a parameter μ_c^* but the symbol μ is later used for the SCDFT Coulomb pseudopotential; the distinct meanings should be clarified.","section":"Appendix B"}],"recommendation":"major_revision","confidential_remarks":"This is a borderline decision. The switch-off tests and internal consistency of the SCDFT calculation are convincing as far as they go, and the qualitative d-wave, SF-driven scenario is plausible. However, the paper's central quantitative claims—Tc agreement, SF dominance, and the sign-changing gap structure—rest on an ALDA/RPA spin susceptibility whose Stoner enhancement and convergence are not documented. This is not a fatal flaw, but it is a load-bearing gap that must be fixed before publication. The referee report should request the missing I value, convergence data, and a sensitivity analysis; these are within the scope of the manuscript. I also recommend that the editors verify the treatment of the Sr doping, since the one-formula-unit cell with unspecified alloying is a second issue that affects the Fermi surface nesting."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Key thing to know: this is the first SCDFT calculation for infinite-layer nickelates that puts electron-phonon, screened Coulomb, and spin-fluctuation pairing on equal footing, and it lands cleanly on SF-driven d-wave. That alone makes it worth a referee's time. The Fermi surface matches ARPES for LaSrNiO, the gap is a two-band dx2-y2 with opposite signs on disconnected pockets, and the switch-off tests are a genuinely nice control: phonons alone give ~1 K, Coulomb suppresses that to ~0.01 K, and adding spin fluctuations gives 7-16 K, close to experiment. That is a coherent, falsifiable scenario, and it is not circular in the obvious sense—no target Tc or gap symmetry was baked into the formalism.\n\nThe soft spots are concentrated in the magnetic kernel. Equation (3) contains a Stoner parameter I that is never given a number. The peak height of chi0 near Q=(pi/a,pi/a) is the whole game, and the paper leans on a sentence saying RPA and ALDA do not differ significantly without showing the comparison. There is no benchmark of chi(q) against neutron or RIXS data, and no convergence or q-grid numbers. On top of that, the 20% Sr substitution is handled in a one-formula-unit cell without saying how the alloy is modeled. These are not red flags by themselves, but they are exactly the details needed to take the quantitative claim that SF is an order of magnitude stronger than EPC and Coulomb. If I sits close to a ferromagnetic instability, the result could be sensitive to small changes in the peak height.\n\nMinor but worth listing: the paper ships no input files or convergence tables, and the RPA/ALDA equivalence is asserted, not demonstrated. Those are fixable in revision.\n\nWho is this for: people working on nickelates specifically, and anyone interested in first-principles routes to unconventional pairing. The qualitative answer is probably right, but the supporting record is incomplete. This paper deserves peer review with explicit requests for the susceptibility details, the Stoner value, the alloy model, and the RPA/ALDA comparison. Not a desk reject.","headline":"First fully ab initio SCDFT for nickelates gives a coherent SF-driven d-wave story; the quantitative core leans on an undocumented Stoner/susceptibility input that needs to be shown before the numbers are trusted.","tokens_in":19913,"tokens_out":1889,"would_cite":true,"duration_ms":25498,"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":"Spin fluctuations, not phonons, drive superconductivity in infinite-layer nickelates, according to ab initio calculations that reproduce the measured transition temperatures and predict a sign-changing d-wave gap.","keywords":["infinite-layer nickelates","d-wave superconductivity","spin-fluctuation pairing","SCDFT","two-band superconductor","B1g gap symmetry","Fermi surface nesting","nodal gap structure"],"falsifier":"A decisive test would be to measure the spin-fluctuation spectrum (e.g., neutron scattering or RIXS) in La0.8Sr0.2NiO2 and look for a peak near Q = (π,π); alternatively, phase-sensitive tunneling could detect the predicted sign change between the central hole pocket and the corner electron pockets; high-resolution ARPES on Nd and Pr nickelates could falsify the Fermi-surface topology that hosts the nesting.","tokens_in":18954,"feed_emoji":"🧲","tokens_out":4892,"duration_ms":51697,"temperature":0.7,"pith_summary":"The paper claims that optimally doped infinite-layer nickelates Re0.8Sr0.2NiO2 (Re = La, Pr, Nd) superconduct through a magnetic pairing mechanism, with a two-band d-wave gap that changes sign between different Fermi surface pockets. Using density functional theory for superconductors, treating electron-phonon coupling, screened Coulomb repulsion, and spin-fluctuation interaction on equal footing, the authors find transition temperatures close to experiments (about 9–16 K) only when spin fluctuations are included; without them, Tc collapses to about 0.01 K. The gap has B1g symmetry, a nodal dx2−y2 form, and opposite signs on the central hole sheet and the corner electron pockets, with its origin traced to nesting peaks in the Lindhard response near (π,π). If correct, the nickelates share the cuprates' magnetic pairing mechanism, and the predicted scanning tunneling spectra can be verified immediately.","feed_headline":"Spin fluctuations drive d-wave pairing in nickelates","feed_subtitle":"Ab initio theory predicts sign-changing gaps on separate Fermi pockets and Tc near 9–16 K.","key_machinery":"The machinery is the density functional theory for superconductors (SCDFT) gap equation, whose kernel combines electron-phonon coupling, screened Coulomb repulsion, and a spin-fluctuation interaction, together with the bare Lindhard susceptibility χ0(q) and the Stoner-enhanced effective interaction V(q) = (3I²/4) χ0(q)/(1 − Iχ0(q)). The Lindhard peaks near Q = (π/a, π/a) are the objects that enforce the sign-reversing d-wave structure, since a repulsive interaction at nesting momentum requires Δk = −Δk+Q, which the B1g basis function x² − y² satisfies on the two Fermi pockets.","core_discovery":"The paper claims that in Re0.8Sr0.2NiO2 (Re = La, Pr, Nd), superconductivity is unconventional and magnetic: the SCDFT gap equation, solved with electron-phonon, screened Coulomb, and spin-fluctuation kernels on equal footing, yields a B1g, sign-changing dx2−y2 gap on two disconnected Fermi-surface pockets, with Tc of 7.3 K, 12.7 K, and 16.1 K for La, Pr, Nd respectively, close to measured values. Computer experiments isolating individual interactions show that phonons alone give about 1 K Tc, which screened Coulomb repulsion almost completely kills, while adding spin fluctuations raises Tc to the experimental scale; on the large central hole pocket the spin-fluctuation pairing strength is a","pith_inferences":["A natural extension is to test whether the predicted pairing survives random Sr disorder by explicit supercell or coherent-potential calculations; the one-formula-unit doping approximation is the softest spot in the doping model.","The same ab initio machinery could be applied to the recently reported Sm-based infinite-layer nickelate to predict its Tc and gap symmetry, giving a falsifiable dome prediction.","If the spin-fluctuation peak near Q = (π,π) is confirmed by neutron scattering or RIXS, the nickelates would become a clean laboratory for d-wave pairing without the pseudogap complications often discussed in cuprates."],"forward_implications":["Electron-phonon coupling alone gives Tc of about 1 K in these nickelates, so any successful theory of their superconductivity must include spin fluctuations as the dominant pairing glue.","The predicted two-band sign-changing gap produces a V-shaped quasiparticle density of states and characteristic scanning tunneling spectra for La and Pr nickelates that can be measured now.","The B1g gap symmetry rules out the alternative s-wave two-gap scenario and gives a concrete target for phase-sensitive experiments.","The calculated Tc values (7.3 K, 12.7 K, 16.1 K for La, Pr, Nd) match the measured dome and could guide further doping studies across the nickelate family."],"supporting_citations":[{"why":"Supplies the SCDFT framework with electron-phonon, Coulomb, and spin-fluctuation kernels used for all Tc and gap calculations.","marker":"[35]"},{"why":"Derives the spin-fluctuation pairing kernel that is the driving interaction in the paper's mechanism.","marker":"[37]"},{"why":"Earlier DFT study showing weak electron-phonon coupling in NdNiO2, the baseline for the paper's EPC-only Tc result.","marker":"[23]"},{"why":"The GW-based competing prediction of s-wave two-gap superconductivity that the paper's d-wave result contrasts with.","marker":"[31]"},{"why":"ARPES Fermi surface of LaSrNiO used to validate the calculated band structure and nesting.","marker":"[44]"},{"why":"Superfluid density evidence for nodal superconductivity in La/Pr nickelates, supporting the d-wave conclusion.","marker":"[28]"},{"why":"STS spectra on NdSrNiO films compared with the calculated quasiparticle density of states.","marker":"[29]"},{"why":"Reports the discovery of superconductivity in infinite-layer nickelates, defining the material family and experimental Tc.","marker":"[15]"}],"fun_headline_variants":["Nickelates: ab initio d-wave pairing from spin fluctuations alone","Ab initio: spin fluctuations, not phonons, cause d-wave in nickelates","Nickelate Tc set by spin fluctuations, not lattice vibrations","d-wave nickelate superconductivity predicted ab initio via spin fluctuations","Spin-fluctuation-mediated d-wave pairing predicted in nickelates"],"cache_read_input_tokens":2688,"weakest_assumption_plain":"The calculation assumes that the random-phase or adiabatic-LDA spin susceptibility faithfully captures the real magnetic response of the strongly correlated Ni 3d electrons, and that representing 20% Sr doping by a single undistorted formula unit preserves the Fermi-surface nesting; if either fails, the predicted d-wave pairing weakens or changes symmetry.","fun_headline_variants_meta":{"raw":{"variants":["Nickelates: ab initio d-wave pairing from spin fluctuations alone","Ab initio: spin fluctuations, not phonons, cause d-wave in nickelates","Nickelate Tc set by spin fluctuations, not lattice vibrations","d-wave nickelate superconductivity predicted ab initio via spin fluctuations","Spin-fluctuation-mediated d-wave pairing predicted in nickelates"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.00091,"raw_usage":{"total_tokens":3865,"prompt_tokens":982,"completion_tokens":2883,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":726,"completion_tokens_details":{"reasoning_tokens":2803}},"tokens_in":726,"tokens_out":2883,"duration_ms":22792,"temperature":1.0,"reasoning_tokens":2803,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-05T00:47:33.521603+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A decisive test would be to measure the spin-fluctuation spectrum (e.g., neutron scattering or RIXS) in La0.8Sr0.2NiO2 and look for a peak near Q = (π,π); alternatively, phase-sensitive tunneling could detect the predicted sign change between the central hole pocket and the corner electron pockets; high-resolution ARPES on Nd and Pr nickelates could falsify the Fermi-surface topology that hosts the nesting.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the SCDFT framework with electron-phonon, Coulomb, and spin-fluctuation kernels used for all Tc and gap calculations."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Derives the spin-fluctuation pairing kernel that is the driving interaction in the paper's mechanism."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Earlier DFT study showing weak electron-phonon coupling in NdNiO2, the baseline for the paper's EPC-only Tc result."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"The GW-based competing prediction of s-wave two-gap superconductivity that the paper's d-wave result contrasts with."},{"cited_title":"Zangwill and P","cited_arxiv_id":null,"evidence_quote":"ARPES Fermi surface of LaSrNiO used to validate the calculated band structure and nesting."},{"cited_title":"Nomura and R","cited_arxiv_id":null,"evidence_quote":"Superfluid density evidence for nodal superconductivity in La/Pr nickelates, supporting the d-wave conclusion."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"STS spectra on NdSrNiO films compared with the calculated quasiparticle density of states."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Reports the discovery of superconductivity in infinite-layer nickelates, defining the material family and experimental Tc."}],"review_version":1}