{"id":"5e9fa5bb-30dc-4a9f-89ce-7f6511e3763b","arxiv_id":"2607.22360","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"Magnetic proximity from a ferromagnetic monolayer lifts the X/Y valley degeneracy in an altermagnetic monolayer, producing non-relativistic valley polarization switchable into four valley-spin states.","lead":"Using density functional theory, this paper shows that stacking ferromagnetic CrP onto altermagnetic V2S2O creates a 53 meV valley polarization in the altermagnet without spin-orbit coupling. Flipping the ferromagnet's magnetization and the altermagnet's Néel vector yields four magnetic configurations, each with a distinct valley-spin state, which could be used for multilevel valleytronic memory.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Four-state claim lacks evidence that the four FM/AM magnetic configurations are stable and independently switchable; only band structures are shown, with no total energies or interlayer exchange coupling.","rationale":"The central claim has two parts: proximity-induced non-relativistic valley polarization (supported by the PbO control, several heterostructures, and the SOC check) and the four-state magnetic-valley coupling (the main novelty). The four-state claim assumes that the FM magnetization and the AM Néel vector are independent degrees of freedom that can be flipped separately. In a van der Waals heterostructure, interlayer magnetic coupling can lock their relative orientation, so this is not a trivial assumption. The manuscript's evidence for the four states is purely electronic: Fig. 5(e-h) shows band structures, but no total energies of the four states, no energy barriers, and no discussion of whether the configurations are local minima or were held fixed by constraints. The reader's U/convergence concern affects the quantitative value of 53.03 meV but not the existence or sign pattern of the four states; therefore it is less load-bearing for the central applied claim. A concrete unconstrained-relaxation calculation would settle whether all four states are physically realizable. Until that check is done, the conditional verdict remains appropriate, though for a different reason than the reader emphasized.","tokens_in":8549,"tokens_out":10417,"duration_ms":117652,"concrete_test":"Starting from each of the four magnetic configurations in Fig. 5(a-d), perform a full unconstrained relaxation (no fixed spin moments) with the same PBE+U/D3 settings and compute the total energy of each converged state. If any of the four configurations relaxes to another one, or if the energy differences exceed the coercivity/anisotropy scale available experimentally, the four-state independence claim fails. Additionally, compute the energy versus relative FM/AM orientation by rotating the AM Néel vector with FM magnetization fixed to extract the interlayer exchange coupling; a single-well energy landscape would indicate the four states are not independently switchable.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's central applied claim is multistate valleytronic storage, which requires the FM magnetization and the AM Néel vector to be independently reversible and the four combined configurations to be addressable. In the Results/Fig. 5 and the Conclusion, the authors show band structures for the four configurations but report no total energies, no magnetic anisotropy, and no energy barriers. Because the FM and AM layers are exchange-coupled across the interface, flipping one magnetic order while holding the other fixed may not be a stable state: if interlayer coupling is strong, states with the 'wrong' relative orientation relax to another configuration, and the four-state pattern in Fig. 5 would reflect constrained DFT artifacts rather than physically realizable states. This is a load-bearing condition for the central claim itself, not a matter of magnitude. The reader's Ueff-convergence concern bears on the 53.03 meV number but not on whether four independent states exist; the stability/independence check is more fundamental.","agreement_with_reader":"disagree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper proposes van der Waals heterostructures combining tetragonal ferromagnetic semiconductors (CrP, CrAs) with altermagnetic monolayers (V2S2O, V2Se2O, Nb2Se2O, Cr2Te2O), and uses DFT (PBE+U with literature Ueff values) to show that the magnetic proximity effect from the FM lifts the X/Y valley degeneracy of the AM without invoking spin-orbit coupling. The central example, CrP/V2S2O, yields a 53.03 meV non-relativistic valley polarization in the AM conduction bands. The authors argue this is universal, demonstrate that the effect scales with interlayer distance, and claim that flipping the FM magnetization and the AM Néel vector produces four independent valley-polarized states suited for multistage valleytronic storage.","tokens_in":8775,"tokens_out":3362,"duration_ms":35323,"significance":"If the result holds, it identifies a SOC-free route to valley polarization and a potential multistate memory concept, extending recent altermagnet valleytronics proposals. The work has clear strengths: standard DFT methodology with no fitted parameters; a control calculation with non-magnetic PbO that supports the magnetic-proximity origin; a check that SOC does not alter the effect; and demonstration in several material combinations. The main significance depends on whether the four configurations are physically switchable metastable states, which the manuscript does not currently establish.","major_comments":[{"comment":"The central applied claim is four independent valley-polarized states for multistage storage. The paper shows band structures for the four FM/AM configurations but reports no total energies, no magnetic anisotropy, and no interlayer exchange coupling. If the FM and AM layers are exchange-coupled, some configurations with reversed FM or reversed Néel order may relax to the ground state; without demonstrating that all four are local minima separated by energy barriers, Fig. 5(e)-(h) may represent constrained states rather than switchable physical states. Please compute total energies for all four configurations, verify metastability relative to the ground state, and estimate switching barriers.","section":"Results and Discussion, Fig. 5; Conclusion"},{"comment":"The headline 53.03 meV valley polarization is obtained with fixed PBE+U parameters (Ueff = 4 eV on V, 3 eV on Cr) and a single k-mesh/cutoff. No U sensitivity, k-mesh, or cutoff convergence is reported. Since CrP has a small indirect gap (41.04 meV) and the exchange splitting is U-sensitive, the magnitude and possibly the sign/ordering of the valley polarization could change. Please provide a U-variation study (e.g., Ueff = 2, 4, 6 eV) and a k-mesh/cutoff convergence check to establish robustness of the 53.03 meV value and of the four-state pattern.","section":"Computational Methods and Results, Fig. 4(b)"},{"comment":"The word 'universal' is used to describe the phenomenon, but the evidence comprises one detailed system (CrP/V2S2O), three additional heterostructures, and a few stacking variants. This is a narrow basis for universality. Either temper the claim (e.g., 'extends to several FM/AM combinations') or provide a symmetry-based argument and a broader materials screen. As written, the universality claim exceeds the evidence presented.","section":"Results and Conclusion, Figs. S4-S6"}],"minor_comments":[{"comment":"Typo: 'spin-orbital coupling' should be 'spin-orbit coupling'. Also the spacing in 'Né el' appears as a non-breaking issue; use 'Néel' consistently.","section":"Abstract/Introduction"},{"comment":"The text states the lattice mismatch between CrP (4.17 Å) and V2S2O (4.03 Å) is approximately 3%; the arithmetic gives about 3.5%. Please check the quoted value.","section":"Results, lattice parameters"},{"comment":"The color scale or intensity scale for layer-resolved band contributions is not defined in the caption. Add a legend or state the isosurface/weight convention.","section":"Fig. 4(c)-(f)"},{"comment":"The four configurations in Fig. 5(a)-(d) are not explicitly labeled in the caption with the FM magnetization direction and the AM Néel vector direction. Defining these symbols would make the four states much clearer.","section":"Fig. 5"},{"comment":"For the interlayer-distance compression/stretching results (Figs. S8-S9), state explicitly whether the internal atomic positions are re-relaxed at each constrained interlayer distance or held fixed. The reported 537.43 meV under 0.5 Å compression should be labeled as a constrained calculation if no relaxation was performed.","section":"Results, interlayer-distance tuning"},{"comment":"Reference [44] is a self-citation and appears in the context of PbO/V2Se2O behavior; please verify that this reference actually reports the cited result and include the relevant comparison in the main text or SI.","section":"References"}],"recommendation":"major_revision","confidential_remarks":"The manuscript is a plausible computational proposal, and the qualitative mechanism is supported by the PbO control and the SOC check. The decisive missing piece is the energetic stability and switchability of the four magnetic configurations; without it, the 'four independent valley-polarized states' claim is not yet established. The U-sensitivity issue also needs to be addressed before the quantitative 53.03 meV figure can be relied upon. These are fixable within the scope of a revision."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague,\n\nThis paper proposes FM/AM van der Waals heterostructures as a SOC-free route to valley polarization. The FM (CrP, CrAs) is a tetragonal ferromagnetic semiconductor; the AM (V2S2O, V2Se2O, Nb2Se2O, Cr2Te2O) has spin-momentum-locked valleys. Magnetic proximity shifts the opposite-spin bands, lifting the X/Y degeneracy. That is the genuinely new piece: proximity from a ferromagnet has been used for TMDs, and altermagnets have been shown to valley-split under strain, but the combination is new and, on the evidence here, physically reasonable.\n\nThe paper does several things right. The PbO control is the best part: swapping in a non-magnetic buffer leaves the AM valleys degenerate, which supports the proximity origin. The layer-resolved bands and the SOC check in the SI reinforce the story. The interlayer-distance dependence (compression boosts the polarization to ~537 meV) is a sensible consistency test. The calculations are standard PBE+U with U values taken from the literature; no fitted parameters are driving the result.\n\nNow the soft spots. The four-state memory claim is not supported. The authors show band structures for the four FM/AM magnetic configurations, but no total energies, no interlayer exchange coupling, and no anisotropy barriers. If the interchange coupling is strong, some of those configurations may not be metastable, and 'independent switching' becomes an artifact. For the multistate storage application, this is load-bearing, not cosmetic. The fix is straightforward: total energies for all four states, the interlayer exchange coupling constant, and ideally a magnetic anisotropy estimate.\n\nSecond, the 'universal' claim rests on four or five heterostructures. That is suggestive, not universal. Third, the headline 53.03 meV value is a single U point; there is no U variation or k-mesh/cutoff convergence shown, so the quantitative number is fragile. The mechanism doesn't depend on that magnitude, but the paper should say so.\n\nThe citation pattern is fine. The self-citation (ref 44) is background, not an input, and ref 45 on the altermagnetic proximity effect is relevant though the comparison is too brief.\n\nMy bottom line: the core mechanism is plausible, and the paper would benefit from a serious referee. It needs major revision before the four-state claim is credible, but it is not a reject on the physics alone. I would send it to review.","headline":"Plausible DFT route to SOC-free valley polarization in FM/AM heterostructures, but the four-state memory claim needs total-energy evidence.","tokens_in":9264,"tokens_out":3655,"would_cite":true,"duration_ms":32820,"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":"A ferromagnet's proximity effect creates four switchable valley states in an altermagnet without spin-orbit coupling.","keywords":["valley polarization","magnetic proximity effect","altermagnet","van der Waals heterostructure","ferromagnetic semiconductor","valleytronics","first-principles calculation","Néel vector"],"falsifier":"Recalculate the CrP/V2S2O band structure with Ueff on V and Cr varied over a realistic range (e.g., 2–6 eV) and with a higher k-mesh or a hybrid functional; if the X/Y splitting changes sign for any reasonable parameter set, the four independent valley states are an artifact of the correlation parameter rather than a robust magnetic-valley coupling.","tokens_in":8454,"feed_emoji":"🧲","tokens_out":4455,"duration_ms":38011,"temperature":0.7,"pith_summary":"The paper predicts that stacking a ferromagnetic semiconductor (CrP or CrAs) on a monolayer altermagnet (V2S2O and related compounds) induces valley polarization in the altermagnet purely through magnetic proximity, with no need for spin-orbit coupling. In the representative CrP/V2S2O stack, the lowermost conduction band splits by about 53 meV between the X and Y valleys, and this splitting grows to 537 meV when the interlayer distance is compressed by 0.5 Å. The authors show that flipping the ferromagnet's magnetization and flipping the altermagnet's Néel vector act as two independent controls, producing four distinct valley-polarized states. The paper argues that the effect is generic across several FM/AM heterostructures, making them a candidate platform for valleytronics-based multistate information storage.","feed_headline":"Ferromagnet proximity splits altermagnet valleys by 53 meV","feed_subtitle":"Flipping the ferromagnet's magnetization and the altermagnet's Néel vector stores four distinct valley states.","key_machinery":"Altermagnet (AM): a collinear magnetic material whose opposite-spin bands are split in momentum space despite zero net magnetization, giving spin-momentum-locked valleys at X and Y without SOC. Magnetic proximity effect: the exchange field leaking from the ferromagnetic layer shifts opposite-spin bands in the AM in opposite directions, lifting valley degeneracy. The two control knobs — FM magnetization direction and AM Néel vector direction — are the binary degrees of freedom that generate the four independent valley-polarized states.","core_discovery":"The central claim is that the magnetic proximity effect of a tetragonal ferromagnetic semiconductor breaks the X/Y valley degeneracy of an adjacent altermagnet monolayer, producing non-relativistic valley polarization — splitting that does not depend on spin-orbit coupling. Using the CrP/V2S2O heterostructure as a test case, first-principles calculations find a 53.03 meV valley polarization in the altermagnet's lowermost conduction band, with layer-resolved bands showing that the valleys come from the V2S2O layer while CrP provides the exchange field. Reversing the CrP magnetization or the V2S2O Néel vector independently flips or reconfigures the valley polarization, giving four independent","pith_inferences":["If the non-relativistic splitting survives in real devices, valley lifetime could be longer than in SOC-based TMD systems, since intervalley scattering mediated by spin-orbit coupling is absent; this is an inference, not a claim of the paper.","The two binary knobs could combine with a third control — interlayer compression — to write and amplify states; a strain-controlled device could toggle between the 53 meV and 537 meV regimes.","The paper's universality argument is based on three additional heterostructures; a sharper test would scan a broader family of tetragonal altermagnets and check whether valley polarization always follows the FM magnetization.","The four-state storage concept implicitly requires that the two magnetic orders switch independently; in reality FM/AM interlayer exchange coupling may bias switching, which is not addressed in the paper."],"forward_implications":["Valley polarization in these FM/AM stacks requires no spin-orbit coupling, opening light-element, high-coherence valleytronic materials.","CrP/V2S2O and similar stacks give four distinct valley-polarized states, so one heterostructure can encode two independent bits, promising multistate valleytronic memory.","The valley splitting is tunable by interlayer distance: 0.5 Å compression raises it from 53 to 537 meV, suggesting strain as a control handle.","Because the effect appears in multiple FM/AM combinations (CrAs/V2Se2O, CrAs/Nb2Se2O, CrP/Cr2Te2O) and in a metastable stacking of CrP/V2S2O, it is likely generic rather than a quirk of one interface.","Flipping FM magnetization flips valley polarization, meaning magnetization direction could be read out optically through valley-selective responses, giving a magneto-valley coupling."],"fun_headline_variants":["Magnet proximity flips altermagnet valleys four ways","Nonrelativistic valley splitting from ferromagnet contact","Four valley states from magnetic proximity in heterobilayer","Magnetic switching writes valley polarization in altermagnet","Ferromagnet-altermagnet stack yields four-valley storage"],"cache_read_input_tokens":2304,"weakest_assumption_plain":"The predicted 53 meV splitting depends on how strongly electron correlations are modeled (the Hubbard U values chosen for V and Cr) and on assuming the most stable stacking; if those values are off, the magnitude and even the pattern of states could change.","fun_headline_variants_meta":{"raw":{"variants":["Magnet proximity flips altermagnet valleys four ways","Nonrelativistic valley splitting from ferromagnet contact","Four valley states from magnetic proximity in heterobilayer","Magnetic switching writes valley polarization in altermagnet","Ferromagnet-altermagnet stack yields four-valley storage"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000389,"raw_usage":{"total_tokens":1846,"prompt_tokens":663,"completion_tokens":1183,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":407,"completion_tokens_details":{"reasoning_tokens":1103}},"tokens_in":407,"tokens_out":1183,"duration_ms":10082,"temperature":1.0,"reasoning_tokens":1103,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-01T04:59:49.592625+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Recalculate the CrP/V2S2O band structure with Ueff on V and Cr varied over a realistic range (e.g., 2–6 eV) and with a higher k-mesh or a hybrid functional; if the X/Y splitting changes sign for any reasonable parameter set, the four independent valley states are an artifact of the correlation parameter rather than a robust magnetic-valley coupling.","supporting_citations":[],"review_version":1}