{"id":"78350827-4841-406c-b4a9-ab9a48fccb0b","arxiv_id":"2507.03368","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"Layered ferroelectric antiferromagnets are shown to combine global spin splitting, valley splitting, and zero net magnetization, with interlayer sliding as a control knob.","lead":"This computational study shows that certain two-layer antiferromagnetic materials with ferroelectric polarization can have both spin and valley polarization at the same time, with no net magnetization. This opens a route to electrically switchable spintronic and valleytronic devices that use antiferromagnets.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The predicted slidetronic control assumes the A-type AFM state remains the ground state at every interlayer shift; if a different magnetic order stabilizes at intermediate stackings, the sign-reversible transport claims lose their equilibrium support.","rationale":"The paper's most emphasized and novel contribution is the reversible, continuous tuning of spin-valley polarization and the associated valley Hall and Nernst conductivities by interlayer sliding. Every such prediction is evaluated in the A-type AFM state at each fixed shift. If that magnetic order is not the ground state at some shifts, the computed splittings and Berry curvatures do not describe the physical system realized in a slidetronics device. This is the single point on which the central claim depends most directly: the symmetry argument in Sec. II guarantees spin and valley splitting within a given magnetic order, but not that the order survives sliding. The stacking-energy curves in Fig. S4, computed only in the AFM state, cannot rule out magnetic phase transitions; they only show which AFM stacking is lowest among AFM candidates. A U-dependence check is also valuable because the reported splittings (up to 123 meV) depend on the correlation correction, and the magnetic state itself may depend on U. No internal inconsistency was found in the symmetry analysis, so the concern is about the scope of the computational sampling rather than a fundamental flaw. The proposed test directly targets this gap and would either support the FE-AFM control narrative or require restricting the claims to the stable stacking window. This matches the reader's identified weakest assumption, so the conditional verdict is appropriate and no adjustment is needed.","tokens_in":15893,"tokens_out":9376,"duration_ms":122679,"concrete_test":"For bilayer Nb3I8, recompute the stacking-energy curves of Fig. S4 along the [100] and [1\\bar{1}0] directions for the A-type AFM, FM, and NM states at U = 2.0, 3.0, and 4.0 eV, using the same DFT-D3 and cutoff settings. If the A-type AFM is not the lowest-energy state at every fractional shift, the slidetronic FE-AFM predictions describe metastable states and the equilibrium control story fails; if it is lowest at all shifts, the qualitative mechanism is supported.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim that spin-valley polarization and its sign can be reversibly tuned by interlayer sliding rests on the assumption that the A-type antiferromagnetic order is the stable magnetic state for every rigid shift considered. The stacking-energy curves in Fig. S4 are computed only in the AFM state, so they do not compare with ferromagnetic, nonmagnetic, or other antiferromagnetic orders. If at some fractional shift the FM state, or another magnetic phase, is lower in energy, then the band splittings and Berry curvature used for the VHE and VNE values are properties of a metastable state, and the sign-reversal under sliding would not occur on the equilibrium adiabatic path. This is not merely a quantitative concern: the ferroelectric polarization and the inequivalence of the two spin sublattices are the two ingredients producing the global spin splitting, and both could change character if the magnetic order changes. The paper reports no U-sensitivity or magnetic-moment convergence tests, so the stability conclusion is not tied to the chosen values of U. The symmetry argument itself is sound and internally consistent; the gap is in the magnetic phase sampling.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper proposes that TP-broken layered ferroelectric antiferromagnets (FE-AFMs) combine altermagnet-like global spin splitting with TP-AFM-like valley splitting. Using DFT+U and Wannier-based transport calculations, the authors focus on bilayer Nb3I8 and show spin splittings up to 123 meV (valence) and 91 meV (conduction), valley splittings up to 93 meV, and valley Hall and Nernst conductivities that reverse sign under ferroelectric switching or interlayer sliding. The same mechanism is claimed for a broader family (Nb3X8, VX2, VSi2X4). The symmetry argument is clean, but the numerical predictions rest on the assumption that the A-type AFM state remains the ground state at every interlayer shift, which is not tested against competing magnetic orders or Hubbard-U variations.","tokens_in":16178,"tokens_out":4637,"duration_ms":63852,"significance":"If the predictions hold, this is a useful conceptual advance: it identifies a concrete symmetry setting in which antiferromagnets can simultaneously exhibit spin polarization in the band structure and valley polarization, with an intrinsic ferroelectric sliding knob. The quantitative predictions (123 meV spin splitting, 93 meV valley splitting, σxy = 1.8 e²/h, αxy = 0.9 α₀) are specific and falsifiable, and the computational workflow is standard and transparent. The main significance depends on the magnetic ground state remaining A-type AFM across the entire sliding path, which is exactly the point that lacks direct evidence.","major_comments":[{"comment":"The slidetronics scenario is computed only in the A-type AFM state: Fig. S4 reports stacking energies along the [100] and [1-10] directions with no comparison to ferromagnetic, nonmagnetic, or other AFM orders, and no magnetic-moment or U-convergence checks are given. Since the central claim is that the spin-valley splittings and sign-reversible VHE/VNE in Fig. 4 occur along an equilibrium sliding path, the calculations must show that the A-type AFM state remains the ground state at each fractional shift. Without such a comparison, the reported transport values may be properties of metastable states and the sign switching would not occur on the adiabatic path.","section":"II, Fig. S4 and Fig. 4"},{"comment":"The Hubbard parameters are fixed to U_eff = 3.0 eV for Nb, 3.0 eV for V, 5.0 eV for Mn, and U = 5.1 eV, J = 0.8 eV for V2Se2O, but no U dependence is reported for the spin splittings, valley splittings, Berry curvature, or transport coefficients. In correlated d-electron systems these quantities can vary strongly with U; a U sweep or a benchmark against experiment for Nb3I8 is needed to establish that the claimed magnitudes and the sign-reversal behavior are robust rather than artifacts of a particular choice.","section":"Appendix A, Eqs. (A1)-(A4)"},{"comment":"The abstract claims demonstration in a broad class (Nb3X8 with X = Cl, Br, I; VX2 with X = S, Se; VSi2X4 with X = N, P), but explicit calculations are shown only for Nb3I8, VS2, and VSi2N4. VSe2 and VSi2P4 are asserted to behave similarly without calculation, and no transport or band-structure results are presented for VS2 and VSi2N4 beyond spin-splitting curves. The universality claim is stronger than the presented evidence.","section":"Abstract and Appendix B, Fig. S2"}],"minor_comments":[{"comment":"The Mott-relation expression appears to omit the factor 1/e: the standard low-temperature form is αxy = -(π² k_B² T)/(3e) σxy'(ε), whereas Eq. (4) lacks 1/e.","section":"Eq. (4)"},{"comment":"There are several typographical errors, including 'camparable' in Section II, 'valance' in the Fig. 3 caption, and 'seeing' in the text near Fig. 3. The phrase 'T Psymmetry' should be 'TP symmetry'.","section":"Throughout"},{"comment":"The 'effective magnetic field' Beff is a relabeling of the computed spin splitting rather than an independently predicted field; the values 1062 T and 786 T should be described as equivalent Zeeman fields, not as new physical magnetic fields.","section":"Section II, Eq. (2)"},{"comment":"The stacking-energy curves show local extrema at n/4 and n/6 shifts, but the paper does not state whether these extrema are minima, maxima, or saddle points, nor does it report energy barriers for the sliding path. A brief clarification of the barrier heights would strengthen the slidetronics discussion.","section":"Appendix B, Fig. S4"}],"recommendation":"major_revision","confidential_remarks":"The manuscript's novelty is adequately situated relative to recent work on layer Hall effects and sliding ferroelectrics, and the symmetry argument is sound. The key technical risk is the unsampled magnetic phase competition under sliding; I would ask the authors to address that before acceptance. The paper is within scope for a condensed-matter physics journal."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The thing to know: this paper gives a clean symmetry-based mechanism for simultaneous spin and valley splitting in fully compensated antiferromagnets with out-of-plane ferroelectric polarization, and shows large, sliding-tunable Berry curvature transport in Nb3I8. The core idea — that when the two spin sublattices are not related by any symmetry operation, spin degeneracy lifts across the BZ while net magnetization stays zero — is sound and nicely framed. That alone makes it worth reading.\n\nWhat's genuinely new: the general FE-AFM framing tying global spin splitting to ferroelectric layer asymmetry, and the demonstration that interlayer sliding can continuously tune and even reverse the spin/valley splittings and the valley-resolved Hall/Nernst conductivities. The authors extend this to Nb3X8, VX2, and VSi2X4 families, though the appendix only actually computes VS2 and VSi2N4; VSe2 and VSi2P4 are guessed by analogy. That overstatement is minor, but it should be fixed.\n\nThe DFT+U, Wannier, and transport machinery is standard and the numbers are plausible. There's no fitted parameter aimed at the target result; the U values come from prior literature. The circularity concern the skeptic raised doesn't land — the splittings are genuine outputs of the calculation.\n\nThe real soft spot is the one the stress test flags: all stacking-energy curves are computed only in the A-type AFM state. There is no check that this magnetic order remains the ground state at intermediate shifts, and no U-sensitivity or magnetic-moment convergence tests. If a different order stabilizes at some stacking, the sign-reversal claims lose equilibrium support. That's a load-bearing gap for the 'slidetronic control' narrative, though not for the basic symmetry argument. It can be addressed with additional calculations, not new theory.\n\nAlso, the paper doesn't ship code or data, which is increasingly expected for computational work of this type.\n\nWho benefits: people working on 2D magnets, altermagnets, valleytronics, and sliding ferroelectrics. It deserves a serious referee — the core mechanism is important enough that the missing magnetic-phase sampling should be requested rather than used to desk reject.\n\nMy recommendation: send it to review, but make the authors test the AFM stability across shifts and report U-dependence. With that added, this would be a solid contribution.","headline":"A clean symmetry argument for spin-valley polarization in ferroelectric antiferromagnets, with a load-bearing assumption about magnetic order under sliding that the paper does not yet test.","tokens_in":16736,"tokens_out":1654,"would_cite":true,"duration_ms":19816,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"A proposed class of ferroelectric antiferromagnets simultaneously lifts spin and valley degeneracy, combining the spin polarization of altermagnets with the valley polarization of TP-symmetric antiferromagnets.","keywords":["ferroelectric antiferromagnet","spin-valley polarization","valley Hall effect","valley Nernst effect","interlayer sliding","Nb3I8","altermagnetism","Berry curvature"],"falsifier":"Look at bilayer Nb3I8 with spin- and angle-resolved photoemission or spin-polarized scanning tunneling spectroscopy: if the valence and conduction bands remain spin-degenerate or the spin-resolved density of states is fully compensated, the central claim fails. Alternatively, a transport measurement of the valley Hall or Nernst signal under ferroelectric switching should show a sign reversal; if neither response changes sign or magnitude with sliding or polarization reversal, the predicted Berry-curvature control is wrong.","tokens_in":15712,"feed_emoji":"🧲","tokens_out":6409,"duration_ms":64564,"temperature":0.7,"pith_summary":"The paper proposes that layered antiferromagnets that are simultaneously ferroelectric—'FE-AFMs'—can spontaneously lift both spin and valley degeneracies, a combination neither conventional TP-symmetric antiferromagnets nor altermagnets achieve on their own. In these materials the two oppositely magnetized sublattices live in different layers and are not related by any symmetry operation, so spin-up and spin-down bands split across the whole Brillouin zone while the valleys at the two K points become nondegenerate. The central demonstration is bilayer Nb3I8, where first-principles calculations give spin splittings up to 123 meV in the valence band and 91 meV in the conduction band, valley splittings up to 93 meV, and Berry-curvature transport with a valley Hall conductivity of 1.8 e2/h and a valley Nernst conductivity of 0.9 alpha0 at 100 K. Because the spin polarization is layer-dependent and tied to the out-of-plane ferroelectric polarization, interlayer sliding tunes the effects and ferroelectric switching reverses them. If correct, this gives a single platform for antiferromagnetic spintronic and valleytronic devices.","feed_headline":"Antiferromagnets that lift spin and valley degeneracy together","feed_subtitle":"Bilayer Nb3I8 splits spin bands by up to 123 meV and switches valley currents by sliding.","key_machinery":"The central object is the TP-broken layered ferroelectric antiferromagnet, exemplified by AA-stacked bilayer Nb3I8 with a breathing kagome lattice and A-type antiferromagnetism. In this phase the two antiparallel spin sublattices are not connected by any symmetry operation, so both spin degeneracy and valley degeneracy are lifted; the out-of-plane ferroelectric polarization makes the spin polarization layer-dependent. The Berry curvature concentrated around the two K valleys, computed from Wannier-based tight-binding Hamiltonians, carries the transport response: opposite-sign curvature at the two valleys produces valley Hall and valley Nernst conductivities whose signs and magnitudes track interlayer sliding and ferroelectric switching.","core_discovery":"The central claim is that time-reversal-parity-broken ferroelectric antiferromagnets combine the spin-polarized band structure of altermagnets with the valley-polarized band structure of TP-symmetric antiferromagnets, while also having an uncompensated spin density of states despite zero net magnetization. The mechanism is demonstrated for AA-stacked bilayer Nb3I8, whose breathing kagome lattice gives out-of-plane ferroelectric polarization and whose A-type antiferromagnetic order leaves the two spin sublattices inequivalent. Because the sublattices occupy different layers, the spin splitting is layer-dependent and follows the out-of-plane polarization; reversing the stacking reverses the spin states and the valley transport signs. The paper further shows that interlayer sliding continuously tunes the splittings and the Berry-curvature hotspots, with the conduction-band valley splitting reversing sign as the dominant layer contribution changes. These features extend to a family of TP-broken bilayers: Nb3X8 (Cl, Br, I), VX2 (S, Se), and VSi2X4 (N, P).","pith_inferences":["The layer-resolved spin polarization suggests a route to electric-field-driven spin-valley memory: since polarization reversal flips the layer contributions, a vertical field could switch the sign of the spin splitting and the valley currents without moving the Neel vector.","The uncompensated spin DOS in a zero-magnetization magnet is a distinguishing signature that could be searched for with spin- and angle-resolved photoemission on cleaved Nb3I8 bilayers.","A natural extension is to test whether the same TP-broken stacking in other compensated magnets, especially those with heavier elements and stronger spin-orbit coupling, pushes the valley splitting and Berry-curvature transport beyond the values reported here.","The Mott-relation link between sigma_xy and alpha_xy means the near-zero Nernst response at one valley is a checkable prediction: a measurement of that valley's anomalous Nernst signal would directly probe the energy derivative of its Hall conductivity."],"forward_implications":["Bilayer Nb3I8 and similar FE-AFMs display spontaneous, global spin splitting without net magnetization, making them usable as antiferromagnetic spin sources that do not produce stray magnetic fields.","Interlayer sliding tunes the spin and valley splittings continuously, and switching the ferroelectric state reverses the signs of the valley Hall and valley Nernst conductivities.","The effective magnetic field implied by the spin splitting reaches about 1062 T at the valence band and 786 T at the conduction band, large enough to matter for spin transport.","Valley-selective transport reaches about 1.8 e2/h and 0.9 alpha0 at 100 K with electron doping, comparable to or larger than known two-dimensional ferromagnets.","The same mechanism is predicted in the Nb3X8, VX2, and VSi2X4 families, suggesting a general design recipe: stack ferrovalley monolayers antiferromagnetically with broken TP symmetry."],"supporting_citations":[{"why":"Establishes that TP-symmetric AFM MnPSe3 has valley polarization but spin degeneracy, the valley-polarized baseline being extended.","marker":"[37]"},{"why":"Introduces altermagnet V2Se2O with C-paired spin-valley locking, the spin-polarized baseline being combined.","marker":"[39]"},{"why":"Provides the intrinsic anomalous valley Hall effect in single-layer Nb3I8, the building block of the bilayer.","marker":"[43]"},{"why":"Shows magnetoelectric coupling in multiferroic bilayer VS2, the basis for layer-dependent spin polarization.","marker":"[49]"},{"why":"Demonstrates nonvolatile electric-field control of spin-valley-layer-polarized anomalous Hall effect in an Nb3I8 bilayer, supporting the switching mechanism.","marker":"[46]"},{"why":"Defines ferrovalley materials, the paradigm this work extends from ferromagnets to antiferromagnets.","marker":"[28]"},{"why":"Supplies the generalized Mott formula connecting Nernst and Hall conductivities used to interpret the valley transport.","marker":"[77]"},{"why":"Provides the effective-magnetic-field estimate for spin splitting in altermagnets, borrowed to quantify the FE-AFM splittings.","marker":"[40]"}],"fun_headline_variants":["Spin and valley meet in ferroelectric antiferromagnets","Sliding layers give spin-valley control in antiferromagnets","Ferroelectric antiferromagnets combine spin and valley splitting","Sliding tunes spin-valley effects in ferroelectric antiferromagnets","Layered ferroelectric antiferromagnets switch spin-valley by sliding"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The picture assumes the bilayer keeps its fully compensated A-type antiferromagnetic order through every interlayer shift, and that the standard Hubbard U corrections used in the calculations are accurate; if sliding changes the magnetic order or the corrections change the band splittings, the predicted magnitudes and switching behavior would shift.","fun_headline_variants_meta":{"raw":{"variants":["Spin and valley meet in ferroelectric antiferromagnets","Sliding layers give spin-valley control in antiferromagnets","Ferroelectric antiferromagnets combine spin and valley splitting","Sliding tunes spin-valley effects in ferroelectric antiferromagnets","Layered ferroelectric antiferromagnets switch spin-valley by sliding"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001063,"raw_usage":{"total_tokens":4514,"prompt_tokens":1057,"completion_tokens":3457,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":673,"completion_tokens_details":{"reasoning_tokens":3359}},"tokens_in":673,"tokens_out":3457,"duration_ms":23751,"temperature":1.0,"reasoning_tokens":3359,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T20:12:54.024298+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Look at bilayer Nb3I8 with spin- and angle-resolved photoemission or spin-polarized scanning tunneling spectroscopy: if the valence and conduction bands remain spin-degenerate or the spin-resolved density of states is fully compensated, the central claim fails. Alternatively, a transport measurement of the valley Hall or Nernst signal under ferroelectric switching should show a sign reversal; if neither response changes sign or magnitude with sliding or polarization reversal, the predicted Berry-curvature control is wrong.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Establishes that TP-symmetric AFM MnPSe3 has valley polarization but spin degeneracy, the valley-polarized baseline being extended."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Introduces altermagnet V2Se2O with C-paired spin-valley locking, the spin-polarized baseline being combined."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the intrinsic anomalous valley Hall effect in single-layer Nb3I8, the building block of the bilayer."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Demonstrates nonvolatile electric-field control of spin-valley-layer-polarized anomalous Hall effect in an Nb3I8 bilayer, supporting the switching mechanism."},{"cited_title":"Tong, S.-J","cited_arxiv_id":null,"evidence_quote":"Defines ferrovalley materials, the paradigm this work extends from ferromagnets to antiferromagnets."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the generalized Mott formula connecting Nernst and Hall conductivities used to interpret the valley transport."},{"cited_title":"Zhang, C","cited_arxiv_id":null,"evidence_quote":"Provides the effective-magnetic-field estimate for spin splitting in altermagnets, borrowed to quantify the FE-AFM splittings."}],"review_version":1}