{"id":"a8665080-0976-44f3-b8be-b1dca0124690","arxiv_id":"2608.11855","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":8.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"Monolayers of M2DO6 (M=Zn, Cd; D=Se, Te) are predicted to be O-2p-ferromagnetic half-metals that become high-Chern-number (C=4) quantum anomalous Hall insulators when spin-orbit coupling is included.","lead":"This paper uses first-principles calculations to predict that certain zinc and cadmium tellurate monolayers become topological insulators with the quantum anomalous Hall effect, driven by magnetism in oxygen orbitals rather than the usual metal atoms. If correct, this opens a new class of oxygen-based magnetic topological materials and a general recipe for making them by removing metal ions.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Central C=4 prediction rests on PBE's O-2p hole magnetism and a 7 meV SOC gap; no hybrid/U cross-check is given, so the phase may be an artifact of self-interaction error.","rationale":"The paper's internal logic is consistent: formal valence counting yields two holes in an O-2p E doublet, the PBE band structure shows a FM half-metal, SOC gaps the Dirac points, and Wannier-based Berry curvature gives a quantized C=4 plateau. The topological invariant computation is standard and there is no obvious algebraic error. The load-bearing fragility is not the Chern counting but the electronic-structure starting point. The authors use only PBE (Ref. [63]); no +U, hybrid, or self-interaction-corrected functional is reported. PBE is known to have large self-interaction errors for localized O-2p holes, and the entire SOC gap is only 7 meV, far below typical errors in relative band positions. Consequently the magnetic ground state, the Dirac crossing arrangement, and the sign/magnitude of the Dirac masses could all change under a more accurate functional. This is a concrete correctness risk rather than a disagreement with consensus. The reader already flagged this; my independent assessment agrees. The proposed HSE06/PBE+U check would settle whether the C=4 phase is robust. I therefore recommend no change to the CONDITIONAL verdict.","tokens_in":10263,"tokens_out":12249,"duration_ms":138044,"concrete_test":"Recompute monolayer Zn2TeO6 (and Cd2TeO6 at 2.5% strain) with the HSE06 hybrid functional at the PBE-relaxed geometry: (1) determine the magnetic ground state and total moment; (2) with SOC, compute the band gap and the Chern number via Wannier interpolation. If the FM state disappears, the global gap closes, or the Chern number changes, the C=4 prediction is not robust to functional choice and the claim should be reframed as conditional on the PBE-level description. A PBE+U calculation with U_eff=3-5 eV on O-2p can serve as a cheaper complementary check.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The claim that M2DO6 monolayers are O-2p ferromagnets with eight massless Dirac points that become a C=4 Chern insulator depends on PBE (Ref. [63]) as the only electronic-structure theory. This is load-bearing in two places. First, the magnetism itself: the two holes in the O-2p E doublet are stabilized by exchange, and PBE's self-interaction error is known to bias the degree of hole localization and magnetic order in oxides (Refs. [45–47] are on d0 oxide ferromagnetism, itself a subtle PBE-sensitive phenomenon). Second, the topological phase: the SOC gap is only ~7 meV (Fig. 3(a)), an order of magnitude smaller than typical PBE errors for oxygen 2p levels, so a hybrid functional or +U correction could easily reverse the sign of the Dirac masses or close the gap. The Wannier-interpolated Berry curvature and the Cloc ~ 0.5 per Dirac point are computed on this PBE Hamiltonian and therefore inherit the functional dependence. No HSE06, PBE+U, or self-interaction-corrected calculation is presented, and the generalization in Table II likewise uses the same protocol. If the O-2p ferromagnetism or the 7 meV gap does not survive a more accurate treatment, the central C=4 QAHE claim is not established.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript proposes that monolayers M2DO6 (M=Zn,Cd; D=Se,Te), derived by deintercalating A cations from honeycomb layered oxides A2M2DO6, realize a quantum anomalous Hall effect driven by O-2p ferromagnetism. Using PBE-based DFT, phonon, and Wannier-interpolation calculations, the authors find a ferromagnetic half-metallic state with two holes in an O-2p E doublet, spin-polarized Dirac points at K/K' and along Γ–K, and, upon spin-orbit coupling, a global gap of about 7 meV with Berry curvature concentrated at the eight gapped Dirac points. Each gapped Dirac point contributes a local Chern number Cloc ≈ 0.5, yielding a quantized anomalous Hall conductance of 4e^2/h. Cd2TeO6 requires about 2.5% tensile strain to align the Dirac points and achieve C=4. The authors generalize the cation-deintercalation strategy to more than 20 oxides, reporting O-2p ferromagnetism and nonzero Chern numbers for several additional slabs including Cd2SbO6 (C=4), Mg2SbO6 (C=1), Cd2BiO6 (C=3), and InO2 (C=1).","tokens_in":10553,"tokens_out":9008,"duration_ms":82827,"significance":"If correct, the paper would establish a new route to the QAHE based on oxygen 2p rather than transition-metal d magnetism, and a high-Chern-number phase C=4 with multiple chiral edge modes. The proposed cation deintercalation strategy for activating O-2p ferromagnetism is an attractive design principle for oxide-based magnetic topology. The paper includes explicit first-principles evidence for phonon stability, magnetic ground-state competition, Berry curvature distributions, and edge-state spectra, and the central Chern number is computed by direct integration of the Wannier-interpolated Berry curvature rather than inferred from the fitted k·p model. The main fragility is that all results rest on a single exchange-correlation functional (PBE) with no +U or hybrid cross-check, and the topological gap of about 7 meV is below typical DFT accuracy.","major_comments":[{"comment":"The central prediction of C=4 QAHE rests entirely on PBE (Ref. [63]) calculations. The O-2p hole ferromagnetism and the 7 meV spin-orbit gap in Fig. 3(a) are both quantities that PBE is known to treat poorly for oxides; self-interaction error can artificially stabilize hole localization on oxygen. Since the Berry curvature, local Chern numbers, and edge states are all computed on this PBE Hamiltonian, a more accurate functional could close the gap or change its sign and invalidate the C=4 phase. Please provide PBE+U or hybrid-functional (e.g., HSE06) calculations for at least Zn2TeO6 and Cd2TeO6, reporting the magnetic moment per O, the size and sign of the SOC gap, and the Chern number. If such checks cannot be performed, the paper should state this limitation explicitly and moderate the claim.","section":"Origin of Magnetism; Band Structures and Topological Properties (Figs. 2-3)"},{"comment":"The Summary states 'monolayer M2DO6 realizes a high-Chern-number QAHE phase with C=4' without qualification, but the Effect of Strain section states that the other three compounds remain gapless even with spin-orbit coupling and require biaxial strain to align the Dirac points. Only Cd2TeO6 under 2.5% tensile strain is explicitly demonstrated to reach C=4. Please state in the Summary and Abstract which members of the family are intrinsic QAH insulators and which require strain, and give the strained results for Zn2SeO6 and Cd2SeO6 in the main text (or explicitly cite the corresponding supplemental figures).","section":"Summary; Effect of Strain"}],"minor_comments":[{"comment":"The phrase 'half-filled O-2p orbital' is imprecise: the two holes occupy the two components of an E doublet at Γ. Please say 'half-filled O-2p doublet' or 'half-filled O-2p manifold'.","section":"Abstract; Origin of Magnetism"},{"comment":"The caption contains the redundant phrase 'high high-symmetry line'; please correct.","section":"Fig. 1(b) caption"},{"comment":"Several references appear in the journal 'Coshare Science' (Refs. [4], [8], and [18]), which is not a standard recognized physics venue; please replace them with more conventional sources or verify their existence. Also, Ref. [35] lists the first author as 'Doung' which is likely a typographical error for 'Duong'.","section":"References"},{"comment":"The main text says that the other three compounds require strain to align the Dirac points, but the strain values are only given for Cd2TeO6 (2.5% tensile). Please list the required strain for each compound in the main text or refer explicitly to the relevant supplemental figures.","section":"Effect of Strain"},{"comment":"The k·p parameters are fitted to the Wannier-interpolated bands, so the local Chern number Cloc ≈ 0.5 is a consistency check rather than an independent derivation. Please emphasize that the C=4 result is obtained from the full Berry curvature integration of the Wannier Hamiltonian (Fig. 3) and not from the fitted model.","section":"k·p model, Eqs. (1)-(3)"},{"comment":"The statement that 'more than 20' oxides exhibit O-2p ferromagnetism is supported only by a reference to Table S2; please add a brief summary in the main text of the screening protocol, the number of materials with and without ferromagnetism, and representative data, so that the generality claim is testable without accessing the supplement.","section":"Generalization of O-2p-induced ferromagnetism; Table II"}],"recommendation":"major_revision","confidential_remarks":"The manuscript reports an interesting prediction of a C=4 QAHE driven by O-2p ferromagnetism, but the reliance on PBE alone and the 7 meV gap make the central claim fragile. The editors may wish to ask the authors for PBE+U or hybrid functional checks before publication. Additionally, several references to the journal 'Coshare Science' (Refs. 4, 8, 18) are not verifiable in standard databases; this is a reference-integrity concern that the editor may want to investigate. The paper otherwise fits the journal's scope and the results are potentially significant if the functional dependence is addressed."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague,\n\nThe new thing here is real: O-2p hole ferromagnetism as a route to a high-Chern-number QAHE, with a concrete materials family (M2DO6 monolayers) and a plausible deintercalation route. I checked the reasoning from the nonmagnetic band structure to the Hund's-rule occupancy argument to the eight Dirac points and the C=4 result. That chain is internally consistent, and the Berry curvature plus edge-state calculation is the right way to support the Chern number. The k.p fit is used for explanation, not as the source of the topology, so I don't see a circularity problem. The strain tuning and the generalization table are useful extras, and the generalization to more than 20 deintercalatable oxides is at least a testable claim.\n\nThe soft spot is exactly where the reader's stress test lands: PBE is the only exchange-correlation functional, and the topologically relevant SOC gap is 7 meV. That is below typical PBE errors for O-2p levels, and PBE's self-interaction error is known to bias hole localization on oxygen. So the O-2p ferromagnetism and the Chern number could both change under hybrid or +U treatment. The authors cite the d0-oxide ferromagnetism literature, which itself is PBE-sensitive, so they know the territory; they just did not do the cross-check. For Cd2SbO6 and InO2 the gaps are larger (11 meV, 20 meV), so at least some members of the family might survive a more accurate functional, but the headline C=4 claim for M2DO6 rests on the 7 meV gap.\n\nMinor points: the claim that M2DO6 monolayers are experimentally accessible is plausible but not demonstrated (exfoliation is mentioned, no exfoliation energy); and one reference list entry (Ref. 4) looks like the wrong venue name. Neither matters much.\n\nWho is this for? People working on oxide magnetism and topological materials prediction. It deserves a serious referee, but the referee should demand PBE+U or hybrid calculations before publication, and ideally a clear statement that the C=4 phase may be functional-dependent. If the authors can show the phase survives even one hybrid calculation for Zn2TeO6, I would treat the prediction as solid. As is, it is a well-argued, interesting but unverified suggestion.\n\nRecommendation: send to peer review, but with the functional question as the make-or-break issue. I would not cite the C=4 claim in my own work until that is settled, though I would cite the deintercalation strategy as a concept.","headline":"A clean, internally consistent PBE prediction of O-2p-driven C=4 QAHE in deintercalated oxides; the physics is credible but the 7 meV gap and lack of functional cross-checks leave the central claim fragile.","tokens_in":11077,"tokens_out":674,"would_cite":false,"duration_ms":9176,"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":"Oxygen 2p magnetism yields Chern number 4 in oxide monolayers","keywords":["quantum anomalous Hall effect","Chern number","oxygen 2p ferromagnetism","oxide monolayers","spin-orbit coupling","Dirac points","cation deintercalation","first-principles calculations"],"falsifier":"A hybrid-functional or DFT+U calculation of monolayer Zn2TeO6 would settle the point: if the oxygen 2p ferromagnetic state is not the ground state, or if the spin-orbit gap closes or changes sign under the corrected functional, the predicted C=4 plateau would not survive. Experimentally, measuring the anomalous Hall conductance of an exfoliated monolayer and finding no plateau at $4e^{2}$/h in the gap would falsify the claim.","tokens_in":10088,"feed_emoji":"🧲","tokens_out":6170,"duration_ms":56082,"temperature":0.7,"pith_summary":"The paper predicts that monolayer oxides M2DO6 (M = Zn, Cd; D = Se, Te), obtained by removing alkali ions from known layered compounds, are ferromagnetic half-metals whose magnetism comes entirely from oxygen 2p holes, not from transition-metal d electrons. In these monolayers, spin-polarized Dirac points appear at two inequivalent momenta, and C3 rotational symmetry multiplies them into eight crossings per Brillouin zone. Spin-orbit coupling opens a small global gap at each crossing, and the eight massive Dirac points together produce a quantized anomalous Hall conductance of $4e^2/h$, a high-Chern-number quantum anomalous Hall state. The paper also shows that cation deintercalation turns more than twenty closed-shell oxides into O-2p ferromagnets, offering a general route from nonmagnetic oxides to magnetic topological materials.","feed_headline":"Oxygen 2p magnetism yields Chern number 4 in oxide monolayers","feed_subtitle":"A predicted family of exfoliable oxides hosts a quantized Hall plateau of 4e^2/h without d-electron magnetism.","key_machinery":"The mechanism is a symmetry-constrained filling of an E-type O-$2p$ doublet: in the nonmagnetic parent, the last two valence electrons occupy a twofold-degenerate representation at the Fermi level and, by Hund's rule, align their spins, producing an O-$2p$-driven ferromagnet without cation moments. The topological machinery is the set of eight spin-polarized Dirac points related by $C_3$ symmetry; an effective two-band $k\\cdot p$ model expanded around each crossing shows that spin-orbit coupling adds a Dirac mass $d_z$, and each gapped Dirac point contributes a local Chern number $C_{\\rm loc}\\approx 1/2$. Summing the eight contributions gives the total Chern number $\\mathcal{C}=4$.","core_discovery":"The central claim is that monolayer M2DO6 realizes an intrinsic high-Chern-number quantum anomalous Hall phase with $\\mathcal{C}=4$, driven by spontaneous ferromagnetism of half-filled O-$2p$ orbitals rather than partially filled $d$ or $f$ shells. Removing the intercalated alkali cations injects two holes per unit cell into the oxygen framework; because the metal cations keep closed-shell $d^{10}$ configurations, the holes reside on oxygen and spin-polarize into an easy-axis ferromagnetic state with a moment of about $2\\,\\mu_B$ per unit cell. In the spin-polarized band structure, two inequivalent Dirac crossings appear, at $K/K'$ and along $\\Gamma$–$K$, and $C_3$ symmetry generates eight symmetry-related Dirac points. Spin-orbit coupling opens a global gap of about 7 meV in Zn2TeO6; each massive Dirac point carries a local Chern number of approximately 1/2, so the total Chern number is $\\mathcal{C}=4$ and the anomalous Hall conductance is quantized at $4e^2/h$, with four chiral edge modes in a ribbon geometry.","pith_inferences":["If O-$2p$ ferromagnetism survives in real samples, the mechanism could widen the search for magnetic topological materials beyond transition-metal compounds, since oxygen-based frameworks are abundant and already synthesized as battery materials.","Because the predicted topological gap is only about 7 meV, confirming the phase experimentally will likely require high-quality exfoliated monolayers and measurement temperatures well below ~80 K; strain or dielectric screening may be needed to stabilize the gap.","A direct testable extension would be to measure the anomalous Hall conductivity as a function of gate voltage in a monolayer device; a plateau at $4e^2/h$ would confirm the half-Chern-number counting, while a different plateau would indicate that the eight Dirac points are not all aligned.","The same deintercalation logic could be applied computationally to other parent compounds with removable cations, such as lithium or potassium analogues, to search for O-$2p$ topological phases with larger gaps."],"forward_implications":["Monolayer Zn2TeO6 should show a quantized anomalous Hall plateau of $4e^2/h$ inside its ~7 meV spin-orbit gap, with four chiral edge channels.","Applying ~2.5% tensile strain to Cd2TeO6 aligns the eight Dirac points in energy and turns the monolayer into a $\\mathcal{C}=4$ high-Chern-number quantum anomalous Hall insulator.","Cation deintercalation is predicted to activate O-$2p$ ferromagnetism in more than twenty closed-shell oxides, including compounds with $d^0$, $d^{10}$, and main-group cations.","Several other deintercalated monolayers (Cd2SbO6, Cd2BiO6, Mg2SbO6, InO3) are predicted to be Chern insulators with Chern numbers 4, 3, 1, and 1, respectively."],"supporting_citations":[{"why":"Shows that d0 oxides can be ferromagnetic via O-2p holes, the mechanism this paper extends.","marker":"[45]"},{"why":"Further evidence that oxygen 2p holes can produce magnetism in oxides without d electrons.","marker":"[46]"},{"why":"Attributes ferromagnetism in d0 oxides to O-2p states, supporting the deintercalation scenario.","marker":"[47]"},{"why":"Reports the layered honeycomb oxide family A2M2DO6 from which the monolayers are derived.","marker":"[53]"},{"why":"Provides the experimental synthesis context for the parent alkali-metal tellurate compounds.","marker":"[54]"},{"why":"Establishes Na2Zn2TeO6 as an experimentally available sodium-ion battery material, making the parent compound accessible.","marker":"[55]"},{"why":"Reviews cation-deintercalatable oxide frameworks, underpinning the proposed deintercalation strategy.","marker":"[56]"},{"why":"The plane-wave density-functional code used for structural relaxation and electronic-structure calculations.","marker":"[62]"},{"why":"The exchange-correlation functional used for all first-principles band-structure and magnetic calculations.","marker":"[63]"},{"why":"The Wannier-based projection used to build the two-band effective Hamiltonian near the Dirac points.","marker":"[67]"}],"fun_headline_variants":["Chern 4 QAHE driven by oxygen 2p ferromagnetism","Oxygen 2p ferromagnetism gives high-Chern QAHE in monolayers","Chern number 4 from oxygen 2p magnetism in oxide monolayers","O-2p spins yield C=4 quantum anomalous Hall effect","No d-electrons: O-2p ferromagnetism grants C=4 QAHE"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The prediction rests on the assumption that the standard density-functional approximation (PBE, without Hubbard U or self-interaction corrections) correctly describes the oxygen 2p holes and the ~7 meV spin-orbit gap; if self-interaction error artificially stabilizes the hole ferromagnetism, the Chern number 4 phase could change or disappear.","fun_headline_variants_meta":{"raw":{"variants":["Chern 4 QAHE driven by oxygen 2p ferromagnetism","Oxygen 2p ferromagnetism gives high-Chern QAHE in monolayers","Chern number 4 from oxygen 2p magnetism in oxide monolayers","O-2p spins yield C=4 quantum anomalous Hall effect","No d-electrons: O-2p ferromagnetism grants C=4 QAHE"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.00082,"raw_usage":{"total_tokens":3640,"prompt_tokens":1046,"completion_tokens":2594,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":662,"completion_tokens_details":{"reasoning_tokens":2490}},"tokens_in":662,"tokens_out":2594,"duration_ms":18423,"temperature":1.0,"reasoning_tokens":2490,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-16T00:23:59.958678+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A hybrid-functional or DFT+U calculation of monolayer Zn2TeO6 would settle the point: if the oxygen 2p ferromagnetic state is not the ground state, or if the spin-orbit gap closes or changes sign under the corrected functional, the predicted C=4 plateau would not survive. Experimentally, measuring the anomalous Hall conductance of an exfoliated monolayer and finding no plateau at $4e^{2}$/h in the gap would falsify the claim.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Shows that d0 oxides can be ferromagnetic via O-2p holes, the mechanism this paper extends."},{"cited_title":"Fischer, N","cited_arxiv_id":null,"evidence_quote":"Further evidence that oxygen 2p holes can produce magnetism in oxides without d electrons."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Attributes ferromagnetism in d0 oxides to O-2p states, supporting the deintercalation scenario."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Reports the layered honeycomb oxide family A2M2DO6 from which the monolayers are derived."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the experimental synthesis context for the parent alkali-metal tellurate compounds."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Establishes Na2Zn2TeO6 as an experimentally available sodium-ion battery material, making the parent compound accessible."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Reviews cation-deintercalatable oxide frameworks, underpinning the proposed deintercalation strategy."}],"review_version":1}