{"id":"a86588bc-24b9-4515-bf98-e5bb372c7068","arxiv_id":"2608.04184","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":12,"one_line_summary":"Hydrostatic pressure from 0 to 40 GPa is predicted to increase the second-neighbor exchange anisotropy in La2O3Mn2Se2, expanding chiral magnon splitting and raising the spin Seebeck conductivity about fourfold at 100 K.","lead":"Using density functional theory and spin-model calculations, the paper predicts that compressing the altermagnet La2O3Mn2Se2 from 0 to 40 GPa strengthens magnetic exchange anisotropy and roughly quadruples a magnon-driven spin Seebeck response. A generalist reader might care because pressure could be a clean, symmetry-preserving knob for controlling both magnetic and electronic transport in one insulating material.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Central prediction assumes Mn remains S=5/2 at 40 GPa, but the cited high-pressure study (Ref. [19]) reports a pressure-driven spin-crossover; the paper never verifies that 40 GPa lies below the crossover.","rationale":"The reader's weakest_assumption is exactly the load-bearing concern I identify: the S=5/2 localized-moment assumption at 40 GPa is threatened by the cited Ref. [19] spin-crossover. The paper's own text draws attention to this by describing Ref. [19] as showing 'an unusual in-plane lattice collapse' while also citing it for structural stability, but it never connects this to the magnetic state. If the spin crossover occurs below 40 GPa, the exchange parameters, magnon spectrum, and spin-Seebeck enhancement all lose their foundation. This concern is more severe than other possible objections (e.g., the assumed τ0=10 ps, or the neglect of interlayer exchange in the magnon calculation) because it attacks the physical validity of the entire spin Hamiltonian at the predicted pressure. The paper does not provide the needed evidence: no Mn moment is reported at 40 GPa, no comparison with Ref. [19]'s crossover pressure, and no spin-state-constrained total-energy analysis. I agree with the reader's CONDITIONAL verdict: the computational workflow is otherwise coherent and the pressure-enhanced |J2a-J2b| is internally consistent, but the missing spin-crossover check is a condition that must be satisfied before the claim is treated as established. The proposed test—fixed-moment DFT or equation-of-state comparison—would settle it directly.","tokens_in":12402,"tokens_out":6946,"duration_ms":76013,"concrete_test":"Compute fixed-spin-moment total energies at the 40 GPa relaxed structure using PBE+U, scanning the Mn moment from 0 to 5 μB; if the S=5/2 state (moment ≈4.5-5 μB) is not the global minimum, or if an unrestricted self-consistent calculation spontaneously converges to a moment below ≈4.5 μB, the central prediction is invalid. Alternatively, compare the calculated pressure-volume curve with the experimental equation of state in Ref. [19] and check whether the in-plane lattice collapse (the spin-crossover signature) occurs at P < 40 GPa; if it does, the paper's 40 GPa results describe a metastable spin state.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The entire magnonic and spin-Seebeck argument depends on the Mn ions retaining localized S=5/2 moments at 40 GPa: exchange parameters (Table I), the linear spin-wave calculation (Methods: 'localized spins with S=5/2'), and the Boltzmann spin-Seebeck formula all presuppose this. The Introduction cites Ref. [19] for structural stability 'up to approximately 53 GPa' but omits that Ref. [19] actually reports an 'unusual in-plane lattice collapse initiated by pressure-driven spin-crossover.' The paper never states the crossover pressure nor demonstrates that 40 GPa is safely below it. If the crossover occurs below 40 GPa, the Mn moment would collapse, the fitted J2a/J2b and δJ2 would be wrong, the chiral magnon splitting and the claimed 3.7x spin-Seebeck enhancement would not occur. The absence of any reported Mn magnetic moment at 40 GPa (e.g., from the self-consistent DFT calculation) makes this impossible to check from the manuscript. This is not an external-consensus disagreement but a failure to address the most relevant experimental constraint on the very pressure range studied.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript combines DFT+U total-energy mapping, spin-Hamiltonian fits, linear spin-wave theory, and Boltzmann transport to predict that hydrostatic pressure from 0 to 40 GPa increases the exchange anisotropy |J2a−J2b| from 1.97 to 9.38 meV in the insulating altermagnet La2O3Mn2Se2. The authors argue that this enhances the chiral magnon splitting and produces a nearly fourfold increase in the longitudinal magnon-driven spin Seebeck conductivity at 100 K, from 3.68×10−1 to 1.36 meV/K, while leaving the symmetry selection rules of the anomalous Hall effect unchanged. The paper also reports pressure-driven redistribution of Berry curvature and sign reversals of the AHC.","tokens_in":12758,"tokens_out":2551,"duration_ms":29196,"significance":"If the central prediction is robust, the paper establishes a concrete symmetry-preserving strategy to simultaneously tune magnonic and electronic transport in an insulating altermagnet, with a clear microscopic mechanism (exchange reconstruction of competing second-neighbor pathways) rather than a purely heuristic tuning claim. The workflow is systematic and includes several praiseworthy elements: exchange parameters are extracted from a large set of magnetic configurations, the interlayer couplings are isolated by configuration subtraction, the magnetic anisotropy is cross-checked with two independent implementations (VASP and FLEUR), and the Monte Carlo and spin-wave analyses use standard, reproducible codes. The main value rests on the quantitative claim at 40 GPa, which is currently sensitive to the high-spin assumption and to the absence of error estimates on the fitted exchange constants.","major_comments":[{"comment":"The paper cites Ref. [19] for structural stability up to about 53 GPa, but that reference reports an unusual in-plane lattice collapse initiated by pressure-driven spin-crossover, as stated in its title. The manuscript never reports the crossover pressure nor verifies that 40 GPa lies below it. Because the magnon spectrum, the spin Seebeck calculation, and the exchange fits in Table I all assume localized Mn ions with S=5/2 (Methods: 'localized spins with S=5/2'), a spin crossover below 40 GPa would invalidate the central prediction. The authors should state the crossover pressure from Ref. [19], report the DFT magnetic moment at 40 GPa, and either demonstrate that the high-spin state survives or restrict the pressure range of the central claim.","section":"Introduction and Methods (magnon spectrum)"},{"comment":"The fitted exchange constants are presented without any uncertainty or sensitivity analysis. The central result is the increase of |J2a−J2b| from 1.97 to 9.38 meV, and the magnon splitting scales approximately as Δε(X)≈1.60δJ2, so the statistical and methodological errors on J2a and J2b are directly propagated into the headline spin Seebeck enhancement. Given that the fits use 'more than 60 magnetic configurations', the authors should provide error bars from the fitting procedure or a sensitivity study with respect to U_eff and the chosen functional, similar to the G/C degeneracy check already reported.","section":"Table I and exchange-mapping subsection"},{"comment":"The paper acknowledges that G-type and C-type interlayer stackings are nearly degenerate at ambient pressure within DFT accuracy, yet the entire magnonic and AHC analysis is performed for the G-type state. Since the claim is that pressure 'preserves the compensated antiferromagnetic ground state', the near-degeneracy at 0 GPa should be quantified (e.g., energy difference in meV/Mn) and the authors should show that the same qualitative conclusions hold for the C-type state or explain why the G-type choice is experimentally mandated at all pressures. As written, the 0 GPa magnon and AHC results could be contingent on a stacking choice that DFT cannot distinguish.","section":"Spin Hamiltonian model and Discussion"}],"minor_comments":[{"comment":"The spin Seebeck result assumes a single constant relaxation time τ0=10 ps for both branches and both pressures, but no justification or sensitivity check is provided; a brief discussion of how τ0 affects the 3.7× enhancement would help.","section":"Equation (3) and Methods"},{"comment":"The text mentions a '63-atom SUPERHEX supercell' and a '2×2×1, 72-atom supercell'; the supercell geometry and the number of independent configurations should be defined more precisely in the main text or the SI, since the reader cannot otherwise assess the conditioning of the exchange fits.","section":"Methods, first-principles calculations"},{"comment":"The sentence introducing Ref. [19] should mention the spin-crossover mechanism explicitly, not only the 'unusual in-plane lattice collapse', because the spin state is precisely the assumption that the pressure-dependent magnon calculation relies on.","section":"Introduction, Ref. [19]"},{"comment":"The color labels for σ_{yz}, σ_{xz}, and σ_{xy} are not visible in the printed description of Fig. 4; please ensure the figure legend is legible and that the correspondence between line color and tensor component is stated in the caption.","section":"Figure 4"}],"recommendation":"major_revision","confidential_remarks":"The spin-crossover issue raised by the reader is, in my reading, the decisive concern and it is properly grounded in the manuscript's own citation of Ref. [19]. I would ask the authors to resolve it before publication, either by showing that 40 GPa is below the crossover or by reformulating the pressure ceiling of the central claim. The lack of error bars on the exchange parameters is a secondary but important issue for a quantitative prediction of this kind."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The one thing to know: this is a competent, standard-methods DFT+spin-model paper with a concrete and testable prediction. The new physics is that hydrostatic pressure increases |J2a-J2b| from 1.97 to 9.38 meV, amplifying the chiral magnon splitting and producing a fourfold enhancement of the spin Seebeck response at 100 K. That mechanism—exchange anisotropy as the pressure lever—is worth engaging with seriously.\n\nWhat the paper does well is real. The exchange mapping is careful: more than 60 configurations for intralayer couplings, dedicated setups for the weak interlayer terms, biquadratic and DM interactions included, and the magnetic anisotropy cross-checked with two codes. They also honestly report the near-degeneracy of G-type and C-type interlayer stacking at ambient pressure, and their Monte Carlo results show pressure strengthens G-type coherence, which is the right kind of supporting evidence. The transport results are derived from fitted exchange parameters, not fitted to the spin Seebeck itself, so the central claim is not circular.\n\nThe soft spot is not minor. The paper assumes S=5/2 localized Mn moments at 40 GPa, but its own cited Ref. [19] reports an unusual in-plane lattice collapse initiated by pressure-driven spin-crossover. The Introduction mentions the collapse but omits the spin-crossover entirely. The manuscript never states the crossover pressure, never reports the Mn magnetic moment at 40 GPa from the self-consistent DFT calculation, and never justifies that 40 GPa lies safely below the crossover. If the crossover occurs below 40 GPa, the exchange parameters, magnon spectrum, and the headline spin Seebeck enhancement are all built on the wrong local-moment state. This is a load-bearing gap, and it is addressable: the authors can compute and report the moment, or shift the prediction to a pressure range where the high-spin state is verified.\n\nSmaller issues: no error bars on the fitted exchange constants, and the absolute spin Seebeck values depend on an assumed tau0=10 ps, so only the pressure-induced ratio should be trusted. The AHC part is a supporting calculation, fine but not central.\n\nWho gets value: people working on altermagnets, magnon transport, or pressure-tuned magnetism. It deserves a serious referee, but the referee should demand the spin-crossover question be resolved before the prediction is treated as established.","headline":"Solid computational prediction with a concrete falsifiable claim, but a gaping hole: the cited high-pressure experiment reports a spin-crossover that could invalidate the S=5/2 assumption at 40 GPa.","tokens_in":13281,"tokens_out":2244,"would_cite":true,"duration_ms":24725,"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":"Pressure boosts exchange anisotropy and quadruples the magnon spin Seebeck response in the insulating altermagnet La2O3Mn2Se2, while preserving the symmetry selection rules for the anomalous Hall effect.","keywords":["altermagnetism","spin Seebeck effect","magnon transport","hydrostatic pressure","exchange anisotropy","chiral magnons","anomalous Hall effect","La2O3Mn2Se2"],"falsifier":"A high-pressure measurement of the Mn local moment (e.g., by x-ray emission spectroscopy or magnetic susceptibility) that detects the onset of a spin crossover below 40 GPa, or a measurement of the longitudinal spin Seebeck coefficient at 100 K and 40 GPa that fails to reach the predicted ~1.36 meV/K, would settle whether the central claim holds.","tokens_in":12221,"feed_emoji":"🧲","tokens_out":8894,"duration_ms":76721,"temperature":0.7,"pith_summary":"Hydrostatic pressure from 0 to 40 GPa is predicted to enhance the inequivalence between two competing second-neighbor exchange interactions in the insulating altermagnet La2O3Mn2Se2, increasing $|J_{2a}-J_{2b}|$ from 1.97 to 9.38 meV while preserving the compensated antiferromagnetic ground state. The enlarged exchange anisotropy widens the momentum-dependent splitting between the two chiral magnon branches, yielding a nearly fourfold increase in the longitudinal magnon-driven spin Seebeck conductivity at 100 K, from $3.68\\times10^{-1}$ to $1.36$ meV/K. In the electronic channel, pressure leaves the magnetic-symmetry selection rules for the anomalous Hall effect unchanged but redistributes the Berry curvature, producing pronounced energy-dependent sign reversals in the anomalous Hall conductivity. Together these results establish exchange anisotropy as the microscopic mechanism by which lattice compression controls both magnonic and electronic transport in a single insulating altermagnet.","feed_headline":"Pressure quadruples the spin Seebeck response in an altermagnet","feed_subtitle":"Exchange anisotropy grows nearly fivefold at 40 GPa, widening chiral magnon splitting and boosting heat-to-spin conversion.","key_machinery":"The central machinery is the spin Hamiltonian with intralayer and interlayer Heisenberg exchange couplings plus biquadratic and Dzyaloshinskii–Moriya terms, fitted to DFT+U total energies by energy mapping. The key object is the pair of crystallographically distinct second-neighbor intralayer exchanges, $J_{2a}$ (linear Mn–O–Mn bridge) and $J_{2b}$ (buckled Mn–Se–Mn bridge), whose inequivalence $\\delta J_2 = |J_{2a}-J_{2b}|$ acts as the control parameter for chiral magnon splitting. Linear spin-wave theory for $S=5/2$ local moments, input to a Boltzmann transport expression for altermagnetic magnons, converts $\\delta J_2$ into the longitudinal spin Seebeck conductivity; the splitting at the $X$ and $Y$ points scales approximately as $\\Delta\\varepsilon(X)\\approx 1.60\\,\\delta J_2$.","core_discovery":"The central claim is that hydrostatic pressure acts as a symmetry-preserving control parameter for both magnonic and electronic transport in the insulating altermagnet La2O3Mn2Se2. Using first-principles calculations and spin-Hamiltonian modeling, the authors find that compressing from 0 to 40 GPa increases the inequivalence between the two second-neighbor intralayer exchange interactions, $|J_{2a}-J_{2b}|$, from 1.97 to 9.38 meV, without altering the signs of any exchange couplings or the compensated G-type antiferromagnetic order. This exchange reconstruction enhances the momentum-dependent splitting of the two chiral magnon branches, producing a nearly fourfold increase in the longitudinal spin Seebeck conductivity at 100 K ($3.68\\times10^{-1}$ to $1.36$ meV/K). In the electronic sector, pressure leaves the magnetic point-group selection rules intact—only $\\sigma_{yz}$ (or $\\sigma_{xz}$) is allowed for $\\mathbf{L}\\parallel x$ (or $y$)—but redistributes the Berry curvature, yielding energy-dependent sign reversals in the anomalous Hall conductivity. The paper identifies exchange anisotropy as the microscopic link between lattice compression and magnon transport, and proposes chemical-pressure substitutions (La$\\rightarrow$Y, Sc, Lu, Yb; Se$\\rightarrow$S) as a practical proxy for applied pressure.","pith_inferences":["One testable extension the authors do not pursue: the predicted scaling $\\Delta\\varepsilon(X)\\approx 1.60\\,\\delta J_2$ suggests that the same exchange-anisotropy mechanism could be used to design other altermagnets with large chiral magnon splitting and enhanced spin Seebeck response at ambient pressure.","If the pressure-driven spin crossover reported in the high-pressure study cited as Ref. [19] begins below 40 GPa, the local moments would shrink and the linear spin-wave and spin Seebeck calculations would no longer apply; this bounds the useful pressure window for the predicted enhancement.","The near-degeneracy of G-type and C-type interlayer stackings at ambient pressure, with pressure favoring G-type correlations, implies that pressure could also be used to stabilize one interlayer magnetic configuration over the other in related layered altermagnets.","A direct experiment measuring the longitudinal spin Seebeck voltage across a La2O3Mn2Se2 film under hydrostatic pressure at 100 K would provide a clean quantitative test of the fourfold enhancement, provided the magnon lifetime and sample geometry are controlled."],"forward_implications":["At 40 GPa, the predicted spin Seebeck conductivity at 100 K reaches 1.36 meV/K, a factor of about 3.7 larger than at ambient pressure, so hydrostatic pressure becomes a quantitative tuning knob for magnonic spin transport.","Because pressure does not alter which anomalous Hall tensor components are symmetry-allowed, the altermagnetic d-wave spin texture and the compensated G-type order are robust under compression; only the magnitude and energy dependence of the Hall response change.","The dominant microscopic origin of the enhanced magnon response is the increase in $|J_{2a}-J_{2b}|$, not a change in the magnetic space group; materials with larger intrinsic second-neighbor exchange inequivalence should show proportionally larger spin Seebeck effects.","Chemical pressure, via substitution of La by smaller nonmagnetic cations (Y, Sc, Lu, Yb) or Se by S, is proposed by the authors as a possible non-hydrostatic route to reproduce the pressure-driven enhancement."],"supporting_citations":[{"why":"Supplies the experimental magnetic structure and G-type antiferromagnetic ordering that the spin Hamiltonian is benchmarked against.","marker":"[13]"},{"why":"Establishes La2O3Mn2Se2 as a correlated insulating d-wave altermagnet, providing the altermagnetic symmetry context for the transport predictions.","marker":"[16]"},{"why":"Reports the two-dimensional d-wave altermagnetic realization and experimental exchange parameters that the authors compare with their fitted values.","marker":"[17]"},{"why":"Gives the microscopic analysis of magnetic interactions (direct vs superexchange) that motivates the pressure sensitivity of the exchange pathways.","marker":"[18]"},{"why":"Documents the high-pressure structural evolution and in-plane lattice collapse that define the experimentally accessible pressure range.","marker":"[19]"},{"why":"Benchmarks the first-principles energy-mapping method used to extract the intralayer and interlayer exchange parameters.","marker":"[20]"},{"why":"Provides the four-state method used to compute biquadratic and Dzyaloshinskii–Moriya interactions in the spin Hamiltonian.","marker":"[22]"},{"why":"Supplies the Boltzmann transport formalism for the longitudinal spin Seebeck effect of magnons in altermagnets, from which the conductivity is calculated.","marker":"[28]"}],"fun_headline_variants":["Pressure quadruples spin Seebeck in altermagnet","Altermagnet's spin Seebeck responds 4x to pressure","Pressure boosts altermagnet heat-to-spin conversion 4-fold","Exchange anisotropy mediates pressure-driven magnon enhancement","Compression enhances altermagnet spin Seebeck 4x"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The prediction depends on the manganese ions keeping their full high-spin local moments up to 40 GPa; the paper cites a high-pressure experiment that finds a lattice collapse initiated by spin crossover, but never establishes that 40 GPa lies below that crossover.","fun_headline_variants_meta":{"raw":{"variants":["Pressure quadruples spin Seebeck in altermagnet","Altermagnet's spin Seebeck responds 4x to pressure","Pressure boosts altermagnet heat-to-spin conversion 4-fold","Exchange anisotropy mediates pressure-driven magnon enhancement","Compression enhances altermagnet spin Seebeck 4x"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000912,"raw_usage":{"total_tokens":3983,"prompt_tokens":1077,"completion_tokens":2906,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":693,"completion_tokens_details":{"reasoning_tokens":2821}},"tokens_in":693,"tokens_out":2906,"duration_ms":21388,"temperature":1.0,"reasoning_tokens":2821,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-08T00:21:03.257863+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A high-pressure measurement of the Mn local moment (e.g., by x-ray emission spectroscopy or magnetic susceptibility) that detects the onset of a spin crossover below 40 GPa, or a measurement of the longitudinal spin Seebeck coefficient at 100 K and 40 GPa that fails to reach the predicted ~1.36 meV/K, would settle whether the central claim holds.","supporting_citations":[{"cited_title":"Alaei, P","cited_arxiv_id":null,"evidence_quote":"Supplies the experimental magnetic structure and G-type antiferromagnetic ordering that the spin Hamiltonian is benchmarked against."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Establishes La2O3Mn2Se2 as a correlated insulating d-wave altermagnet, providing the altermagnetic symmetry context for the transport predictions."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Reports the two-dimensional d-wave altermagnetic realization and experimental exchange parameters that the authors compare with their fitted values."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Gives the microscopic analysis of magnetic interactions (direct vs superexchange) that motivates the pressure sensitivity of the exchange pathways."},{"cited_title":"Garcia-Gassull, A","cited_arxiv_id":null,"evidence_quote":"Documents the high-pressure structural evolution and in-plane lattice collapse that define the experimentally accessible pressure range."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Benchmarks the first-principles energy-mapping method used to extract the intralayer and interlayer exchange parameters."},{"cited_title":"Mosleh and M","cited_arxiv_id":null,"evidence_quote":"Provides the four-state method used to compute biquadratic and Dzyaloshinskii–Moriya interactions in the spin Hamiltonian."},{"cited_title":"pressure- tunable electronic and magnonic transport in altermagnet La 2O3Mn2Se2","cited_arxiv_id":null,"evidence_quote":"Supplies the Boltzmann transport formalism for the longitudinal spin Seebeck effect of magnons in altermagnets, from which the conductivity is calculated."}],"review_version":1}