{"id":"9d95674d-ce21-4340-b211-8d6fc165f59e","arxiv_id":"2506.14314","paper_version":1,"verdict":"REJECT","confidence":"HIGH","novelty_score":4.0,"correctness_risk":"high","formal_verification":"none","parameter_count":2,"one_line_summary":"DFT+U shows doping suppresses magnetism in predicted d9 multiferroics, which the author takes as evidence they might become noncentrosymmetric high-temperature superconductors, although no superconducting state is shown.","lead":"This paper proposes that chemically doping predicted d9 multiferroics such as SnCuO2, PbCuO2, and BiNiO2 could produce noncentrosymmetric high-temperature superconductors. It reports DFT+U calculations showing that doping suppresses antiferromagnetic order in two materials, but no superconductivity is demonstrated.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Doping suppresses AFM order in the DFT+U data, but the polar P4mm distortion that supplies the noncentrosymmetric property is never checked at finite doping; if carriers destroy ferroelectricity, the central proposal collapses.","rationale":"The reader's strongest claim correctly identifies the gap between the DFT+U magnetic suppression results and the conclusion of high-Tc superconductivity. The reader's weakest assumption focuses on whether suppressing AFM order is sufficient to produce superconductivity. My concern is more specific and structurally upstream: even before discussing pairing, the doping calculations do not verify that the polar P4mm distortion remains the ground state when carriers are added. Since the noncentrosymmetric property is the paper's distinctive selling point, this is load-bearing. It is not a disagreement with consensus or a request for impossible proof; it is a concrete stability check that the authors' own DFT framework can perform. I therefore agree with the reader's REJECT verdict and recommend no adjustment.","tokens_in":4915,"tokens_out":2231,"duration_ms":24194,"concrete_test":"Using the same DFT+U setup as Section II.D, recompute for each doping concentration reported in Figs. 5-6 for PbCuO2 and BiNiO2: (i) the fully relaxed structure under P4mm symmetry and the resulting phonon frequencies, especially the A2u polar mode; (ii) the spontaneous polarization via Berry-phase calculations. If at any doping where G-AFM is suppressed the A2u mode becomes imaginary or the polarization drops below about 0.1 C/m^2, the noncentrosymmetric platform is not realized at that doping; if the polar phase persists, the proposal would gain needed support.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's central claim is that doped d9 multiferroics can reliably yield noncentrosymmetric high-Tc superconductors. The only new evidence is the DFT+U suppression of AFM order in BiNiO2 and PbCuO2 with doping (Figs. 5-6). This is an order-parameter suppression calculation, not a superconductivity calculation, and it rests on an unstated assumption: that the polar P4mm structure, which is the actual source of inversion-symmetry breaking, remains stable when carriers are introduced. The manuscript never reports doped ionic positions, lattice parameters, phonon stability, or calculated polarization at finite doping. Doped carriers could screen the lone-pair-driven polar distortion, soften the A2u mode, and drive a transition back to the nonpolar P4/mmm phase, thereby eliminating the noncentrosymmetric property that motivates the proposal. Moreover, 'suppressed AFM order implies superconductivity' is an analogy, not a derivation; cuprate parents show that magnetism suppression is necessary but nowhere near sufficient for high-Tc superconductivity. Thus the central conclusion is unsupported by the calculations shown, even if the underlying materials-by-design hypothesis is plausible and testable.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper proposes that chemically doped d9 multiferroics (SnCuO2, PbCuO2, BiNiO2) with the polar P4mm structure can serve as noncentrosymmetric high-temperature superconductors. It reviews the authors' prior predictions of these multiferroic parent compounds and presents new DFT+U calculations for doped BiNiO2 and PbCuO2, showing that the energy difference between antiferromagnetic (AFM) and ferromagnetic (FM) states decreases with doping and that magnetic moments evolve non-monotonically (Figs. 5-6). On this basis and by analogy to doped cuprates and nickelates, the conclusion states that it is reliable to seek superconductivity in doped d9 multiferroics and that noncentrosymmetric high-Tc superconductors can be obtained. The manuscript contains no calculation of a superconducting order parameter, no pairing strength, no Tc estimate, and no experimental data. The central claim is therefore unsupported by the evidence presented.","tokens_in":5290,"tokens_out":3848,"duration_ms":41055,"significance":"If the design strategy were validated, the paper would open a genuinely new class of noncentrosymmetric high-Tc superconductors with potentially mixed singlet-triplet pairing, which is of considerable importance. The strength of the manuscript is its concrete DFT+U data showing doping-induced suppression of AFM order in two candidate compounds, and its explicit link to existing d9 parent compounds of cuprates and nickelates. The weakness is that the entire case for superconductivity rests on an analogy, not on a demonstration; magnetic order suppression is a necessary but far from sufficient condition for high-Tc superconductivity. The polar P4mm structure, which provides the inversion-symmetry breaking, is not checked for stability under doping. Thus the significance currently depends on an untested assumption rather than on results shown in the paper.","major_comments":[{"comment":"The central claim of the title and conclusion, namely that doped d9 multiferroics are noncentrosymmetric high-temperature superconductors, is not supported by any superconductivity-related calculation or measurement. The only new evidence, the DFT+U results in Figs. 5 and 6, concerns the doping dependence of AFM-FM energy differences and magnetic moments. These results at most indicate a weakening of magnetic order; they do not establish metallicity, pairing, or a finite Tc. The cuprate and nickelate examples cited in the paper themselves show that suppressing antiferromagnetism is a prerequisite but not a predictor of superconductivity. This is a load-bearing gap: the title and conclusion overstate what the calculations demonstrate.","section":"Sec. III, Title"},{"comment":"The proposed physics depends entirely on the noncentrosymmetric P4mm polar structure, yet the manuscript never verifies that this structure remains stable upon doping. Doped carriers can screen the lone-pair-driven ferroelectric distortion, soften the A2u polar mode, and drive a transition back to nonpolar P4/mmm, which would eliminate the inversion-symmetry breaking that motivates the proposal. The paper does not report doped ionic positions, lattice parameters, phonon stability, or calculated polarization at any finite doping concentration. Without such checks, the central premise that the doped materials are noncentrosymmetric is unverified.","section":"Sec. II.D, Figs. 5-6"},{"comment":"The argument from analogy assumes that the d9 charge-transfer physics of cuprate and nickelate parent compounds transfers unchanged to the polar P4mm framework with heavy Sn2+/Pb2+/Bi3+ cations. This assumption is not tested. The strong spin-orbit coupling and the ferroelectric distortion could substantially alter the effective low-energy Hamiltonian, changing hoppings, exchange couplings, and the nature of the doped metallic state. The manuscript contains no model or calculation showing that a cuprate-like superconducting pairing survives in this structure. The claim that 'it is reliable to seek superconductivity' is thus an extrapolation, not a result.","section":"Sec. II.E"}],"minor_comments":[{"comment":"The phrase 'the Cu-3dx2-y2 band lies 0.37 eV above the O-2p valence band maximum (VBM)' is unclear; please specify whether this is a charge-transfer gap or an energy offset and define the reference level.","section":"Sec. II.C"},{"comment":"The axis labels and doping units (e/f.u.) should be defined in the captions, and the legend entries are too small to read at normal print size.","section":"Figs. 5-6"},{"comment":"The subsection contains the phrase 'Mott Insulator Basis' with inconsistent capitalization; it should be corrected to a normal sentence.","section":"Sec. II.D"},{"comment":"The phrase 'it is reliable to seeking superconductivity' is ungrammatical; it should read 'it is reliable to seek superconductivity' or 'one can reliably seek superconductivity.'","section":"Sec. II.E, Sec. III"}],"recommendation":"reject","confidential_remarks":"The manuscript is effectively a perspective or proposal supported by a modest DFT+U study, but its title and conclusion assert a result that the evidence does not establish. The missing pieces, namely an actual superconductivity calculation and a check of the polar phase stability under doping, are substantial additions rather than local revisions. The authors may wish to resubmit the work as a perspective article or after incorporating such evidence. I would also note the heavy reliance on the authors' own prior predictions; this is understandable given the continuity of the research program, but the current manuscript does not yet provide the independent validation that would make the central claim convincing."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Here's the short version. The paper is a proposal, not a demonstration. What's actually new is a set of DFT+U calculations showing that electron and hole doping reduce the G-AFM vs FM energy difference in PbCuO2 and BiNiO2 (Figs. 5-6). That is a real computational dataset and it does show the expected trend: doping weakens the magnetic order. The idea that a polar P4mm d9 material could give you a noncentrosymmetric superconductor is worth taking seriously; it's a natural extension of the author's earlier work and of the nickelate/cuprate doping playbook.\n\nThe problem is the gap between what is calculated and what is claimed. The title and conclusion say these doped d9 multiferroics will give noncentrosymmetric high-temperature superconductors. There is no calculation of pairing, no estimate of Tc, no superconducting order parameter, not even a check that the doped Fermi surface is plausible for unconventional pairing. The DFT+U data shows only that AFM order is suppressed, which is a necessary but not sufficient condition. The stress-test note is on target: the polar P4mm structure is the actual source of broken inversion symmetry, and the paper never checks whether that distortion survives carrier doping. If the A2u mode softens and the structure relaxes back to P4/mmm, the whole proposal collapses. That's not a minor omission; it's a load-bearing assumption.\n\nThe author does at least frame the work as a strategy and says 'we argue this question' in the introduction, so it's not incoherent. But the conclusion drops the hedging and makes a flat assertion. The citation pattern is fine: the author cites their own prior predictions, which is appropriate when those are the material candidates, and the external refs (NdNiO2, BiNiO3, LaNiO2/CaCuO2 comparison) are standard.\n\nMy read: as a research result it should be rejected. The central claim is unsupported. As a speculative proposal, with the overclaim stripped and the structural stability question addressed, it could be a useful contribution for people hunting noncentrosymmetric superconductors. If the journal has a place for clearly-labeled proposals, send it to one referee to confirm the missing pieces; otherwise desk-reject with an invitation to resubmit once the polar distortion is checked at finite doping or a pairing calculation is attempted.","headline":"A testable materials-by-design hypothesis, but the paper sells an analogy as a result; the only new data is a DFT+U magnetic suppression calculation.","tokens_in":5643,"tokens_out":2725,"would_cite":false,"duration_ms":28330,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["74.20.-z","74.25.-q","75.85.+t"],"model":"deepseek-v4-flash","headline":"Doped $d^9$ multiferroics are proposed as a route to noncentrosymmetric high-temperature superconductors.","keywords":["d9 multiferroics","noncentrosymmetric superconductivity","charge-transfer insulators","spin-orbit coupling","Mott insulators","nickelate superconductors","cuprate superconductors","lone-pair ferroelectricity"],"falsifier":"Synthesize hole- or electron-doped BiNiO$_2$, SnCuO$_2$, or PbCuO$_2$ films and measure resistivity and DC susceptibility at low temperature: a superconducting transition with zero resistance and Meissner expulsion in the polar P4mm phase would validate the claim, whereas complete doping-induced loss of antiferromagnetic order with no superconducting transition would falsify it.","tokens_in":4706,"feed_emoji":"⚡","tokens_out":9918,"duration_ms":89655,"temperature":0.7,"pith_summary":"This paper argues that a class of ferroelectric insulators with a $d^9$ electronic configuration, namely SnCuO$_2$, PbCuO$_2$, and BiNiO$_2$, can be turned into noncentrosymmetric high-temperature superconductors by chemical doping. These materials combine broken inversion symmetry with the same charge-transfer and Mott physics found in the parent compounds of cuprate and nickelate superconductors. The paper's own DFT+U calculations show that doping weakens their antiferromagnetic order, the precondition for superconductivity in those families. If the argument holds, it offers a materials-by-design route to superconductors in which spin-orbit coupling should allow mixed singlet-triplet pairing.","feed_headline":"Doping d9 multiferroics could yield high-Tc superconductors","feed_subtitle":"Doping suppresses magnetic order, preserving broken inversion symmetry for unconventional pairing.","key_machinery":"The central object is the $d^9$ multiferroic: a half-filled $d^9$ band carried by Cu$^{2+}$ or Ni$^+$ placed in a polar P4mm lattice by stereochemically active lone-pair cations such as Sn$^{2+}$, Pb$^{2+}$, or Bi$^{3+}$, giving a ferroelectric Mott or charge-transfer insulator with G-type antiferromagnetic order. The argument's working parts are the DFT+U doping calculations, which track the antiferromagnetic-ferromagnetic total-energy difference and site moments versus electron or hole concentration, and the symmetry argument that broken inversion symmetry plus strong spin-orbit coupling permits mixed singlet-triplet superconducting pairing once doping metallizes the system.","core_discovery":"On its own terms, the paper's claim is a design principle: $d^9$ multiferroics combine the broken inversion symmetry of a polar P4mm lattice with the $d^9$ charge-transfer/Mott physics of cuprate and nickelate parents, and chemical doping weakens their antiferromagnetic order. DFT+U calculations for BiNiO$_2$ and PbCuO$_2$ show that the G-type antiferromagnetic versus ferromagnetic energy difference approaches zero with doping, with site magnetic moments evolving systematically, which the paper reads as the precursor to metallicity and superconductivity. The stated conclusion is that it is reliable to seek superconductivity in doped $d^9$ multiferroics, yielding noncentrosymmetric high-temperature superconductors with mixed singlet-triplet pairing. The paper reports no superconducting transition; the discovery is the strategy and its supporting electronic-structure evidence.","pith_inferences":["A companion calculation the paper does not report would extract the pairing symmetry and gap structure from the doped DFT+U bands; a sign-changing order parameter would make the proposal testable within the same framework.","Because the parent phases are ferroelectric, any superconducting state, if found, could in principle be switched or tuned by an applied electric field, a control knob absent in centrosymmetric cuprates and nickelates.","The lone-pair design may be portable to other $d^9$ cations such as Ag$^{2+}$ or Pd$^+$, giving a family of polar charge-transfer systems with tunable correlation strength and spin-orbit coupling."],"forward_implications":["If realized, the superconductivity would be noncentrosymmetric, so spin-orbit coupling would mix singlet and triplet components of the order parameter.","Both electron and hole doping appear able to suppress the antiferromagnetic parent state, widening the experimental search space in these materials.","The cuprate-like exchange couplings in SnCuO$_2$ and PbCuO$_2$, around 76 to 82 meV, indicate magnetic fluctuations strong enough to mediate pairing.","BiNiO$_2$ thin films, obtainable by reducing BiNiO$_3$ as NdNiO$_2$ was, are the most direct experimental test of the proposal."],"supporting_citations":[{"why":"Supplies the predicted BiNiO$_2$ parent: a polar P4mm Mott multiferroic with G-type antiferromagnetic order and a 0.5 eV gap.","marker":"[1]"},{"why":"Establishes SnCuO$_2$ and PbCuO$_2$ as charge-transfer $d^9$ multiferroics with lone-pair ferroelectricity and antiferromagnetic ground states.","marker":"[2]"},{"why":"Reports superconductivity in doped infinite-layer nickelate NdNiO$_2$, the experimental precedent for reducing perovskite oxides into $d^9$ superconducting parents.","marker":"[3]"},{"why":"Provides the structural and valence-transition data for BiNiO$_3$ used to argue that BiNiO$_2$ should be experimentally accessible.","marker":"[4]"},{"why":"Shows the electronic-structure similarity between LaNiO$_2$ and CaCuO$_2$, supporting the transfer of cuprate doping physics to nickelate-derived $d^9$ systems.","marker":"[6]"}],"fun_headline_variants":["Doped d9 multiferroics: a path to noncentrosymmetric high-Tc","Noncentrosymmetric superconductivity from doped d9 multiferroics","Chemical doping of d9 multiferroics may enable high-Tc pairing","Doping d9 multiferroics could produce noncentrosymmetric superconductors"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The paper assumes that suppressing antiferromagnetic order in these ferroelectric $d^9$ insulators is sufficient to produce high-temperature superconductivity, meaning the polar distortion does not destroy the pairing mechanism inherited from cuprates and nickelates.","fun_headline_variants_meta":{"raw":{"variants":["Doped d9 multiferroics: a path to noncentrosymmetric high-Tc","Noncentrosymmetric superconductivity from doped d9 multiferroics","Chemical doping of d9 multiferroics may enable high-Tc pairing","Doping d9 multiferroics could produce noncentrosymmetric superconductors"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000759,"raw_usage":{"total_tokens":3321,"prompt_tokens":841,"completion_tokens":2480,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":457,"completion_tokens_details":{"reasoning_tokens":2393}},"tokens_in":457,"tokens_out":2480,"duration_ms":19836,"temperature":1.0,"reasoning_tokens":2393,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-07T00:16:44.936546+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Synthesize hole- or electron-doped BiNiO$_2$, SnCuO$_2$, or PbCuO$_2$ films and measure resistivity and DC susceptibility at low temperature: a superconducting transition with zero resistance and Meissner expulsion in the polar P4mm phase would validate the claim, whereas complete doping-induced loss of antiferromagnetic order with no superconducting transition would falsify it.","supporting_citations":[{"cited_title":"From a superconductor NdNiO$_2$ to a Mott multiferroic BiNiO$_2$","cited_arxiv_id":"2302.00172","evidence_quote":"Supplies the predicted BiNiO$_2$ parent: a polar P4mm Mott multiferroic with G-type antiferromagnetic order and a 0.5 eV gap."},{"cited_title":"Copper-based charge transfer multiferroics with a $d^9$ configuration","cited_arxiv_id":"2306.01361","evidence_quote":"Establishes SnCuO$_2$ and PbCuO$_2$ as charge-transfer $d^9$ multiferroics with lone-pair ferroelectricity and antiferromagnetic ground states."},{"cited_title":"Azuma et al., Pressure -induced intermetallic valence transition in BiNiO 3, J","cited_arxiv_id":null,"evidence_quote":"Provides the structural and valence-transition data for BiNiO$_3$ used to argue that BiNiO$_2$ should be experimentally accessible."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Shows the electronic-structure similarity between LaNiO$_2$ and CaCuO$_2$, supporting the transfer of cuprate doping physics to nickelate-derived $d^9$ systems."}],"review_version":1}