{"id":"73685a9a-f000-4bb6-9ffb-dab7b315d090","arxiv_id":"2507.07071","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":7.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"Exciton motion in CrSBr is driven by incoherent magnon currents, producing enhanced isotropic transport near the Neel temperature and superdiffusive spreading in bilayers.","lead":"In the van der Waals antiferromagnet CrSBr, excitons propagate faster and more isotropically near the Neel temperature, with superdiffusive motion in bilayers and transient cloud contraction at low temperatures. These behaviors point to drag from laser-induced magnon currents rather than standard exciton diffusion.","discovery_kind":"new_application","skeptic_critique":{"model":"grok-4.3","headline":"No quantitative model or simulation links expected magnon currents to the specific observed exciton cloud dynamics","rationale":"The reader's weakest assumption correctly isolates the interpretive step. Because the paper offers only qualitative attribution rather than a falsifiable forward model, the concern is load-bearing for the claim that magnon currents are the primary driver. A single numerical check of the proposed mechanism against the data would directly test whether the interpretation holds or whether conventional channels remain viable.","tokens_in":1751,"tokens_out":339,"duration_ms":14925,"concrete_test":"Construct a minimal 2D exciton-magnon drag model (exciton continuity equation with an additional velocity term proportional to local magnon current density, using measured magnon dispersion and estimated exciton-magnon matrix element from the paper's own parameters); numerically propagate an initial Gaussian cloud for the reported pump fluences and compare the resulting FWHM(t) and anisotropy to the experimental traces in the main figures. If the simulated enhancement near TN and the low-T transient contraction fall outside 30% of measured values, the magnon-drag interpretation is not yet supported.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The central claim requires that laser-induced incoherent magnon currents produce drag forces whose magnitude and temperature dependence reproduce the reported ultrafast isotropic propagation, low-T contraction/expansion, and superdiffusion. The manuscript interprets the data as defying conventional mechanisms but provides no microscopic rate calculation, Boltzmann transport simulation, or even order-of-magnitude estimate of the magnon-exciton scattering length or drag velocity that would be needed to match the measured spatial profiles versus time, temperature, and layer number.","agreement_with_reader":"agree"},"referee_report":{"model":"grok-4.3","summary":"The manuscript reports time-resolved photoluminescence measurements on the van der Waals antiferromagnet CrSBr demonstrating ultrafast, nearly isotropic exciton propagation that is substantially enhanced near the Néel temperature, transient contraction and expansion of exciton clouds at low temperatures, and superdiffusive transport in bilayer samples. The authors interpret these observations as arising from drag forces exerted by laser-induced currents of incoherent magnons rather than conventional exciton diffusion or phonon-assisted processes, and propose that exciton-magnon scattering provides a general route to imprint spin-excitation properties onto optical quasiparticle motion.","tokens_in":1854,"tokens_out":624,"duration_ms":49544,"significance":"If the magnon-drag interpretation is confirmed, the work would establish a concrete experimental link between incoherent spin excitations and exciton transport in a magnetic semiconductor, supplying temperature- and layer-dependent data that could guide microscopic theories of exciton-magnon coupling. The reported signatures are potentially valuable for magneto-optical control schemes, though the absence of a quantitative model or explicit exclusion of alternatives currently limits the strength of the central claim.","major_comments":[{"comment":"The central interpretation—that the observed ultrafast isotropic propagation, low-T cloud dynamics, and superdiffusion 'largely defy description by commonly known exciton transport mechanisms' and are instead produced by magnon currents—lacks any microscopic rate calculation, Boltzmann transport simulation, or order-of-magnitude estimate of the magnon-exciton scattering length or drag velocity needed to reproduce the measured spatial profiles versus time, temperature, and layer number (abstract and results/discussion sections).","section":"Abstract and Discussion"},{"comment":"Alternative mechanisms (phonon drag, defect trapping, or conventional diffusion) are invoked as insufficient but are not quantitatively compared or experimentally excluded; targeted controls such as magnetic-field dependence, isotopic substitution, or defect-density variation would be required to make the magnon-drag assignment load-bearing (results and discussion sections).","section":"Results and Discussion"},{"comment":"The temperature-dependent enhancement at the Néel temperature and the reported propagation speeds are presented without quantitative error bars, fitting details, or statistical analysis of the time-resolved maps, which weakens the claim that the behavior is substantially enhanced and distinct from conventional mechanisms (experimental data presentation).","section":"Experimental Results"}],"minor_comments":[{"comment":"The abstract would benefit from a brief statement of the excitation conditions (wavelength, fluence) and the definition of 'superdiffusive' used for the bilayer data.","section":"Abstract"},{"comment":"Figure captions and axis labels for the exciton cloud images should explicitly indicate the time delays and temperatures corresponding to each panel to improve readability.","section":"Figures"}],"recommendation":"major_revision","confidential_remarks":"The manuscript is a reasonable fit for cond-mat.mes-hall but the interpretation remains largely qualitative; a revised version with even a minimal transport model would substantially strengthen the case for publication."},"author_rebuttal":{"model":"grok-4.3","summary":"We thank the referee for the careful reading and constructive comments on our manuscript. We address each major comment point by point below. Where possible, we have revised the manuscript to incorporate additional analysis and clarifications while maintaining the integrity of our experimental findings and interpretation.","responses":[{"response":"We acknowledge the value of a quantitative microscopic model. In the revised manuscript we have added an order-of-magnitude estimate in the discussion section that relates the observed propagation speeds (on the order of 10^5 cm/s) to expected magnon velocities and laser-induced magnon currents in CrSBr. A full Boltzmann transport simulation lies beyond the scope of this primarily experimental study, but the pronounced temperature dependence peaking at the Néel temperature and the layer-number dependence (enhanced superdiffusion in bilayers) already provide strong qualitative and semi-quantitative support for magnon drag over conventional mechanisms. We have expanded the relevant paragraphs to make this estimate explicit.","revision_made":"partial","referee_comment":"[Abstract and Discussion] The central interpretation—that the observed ultrafast isotropic propagation, low-T cloud dynamics, and superdiffusion 'largely defy description by commonly known exciton transport mechanisms' and are instead produced by magnon currents—lacks any microscopic rate calculation, Boltzmann transport simulation, or order-of-magnitude estimate of the magnon-exciton scattering length or drag velocity needed to reproduce the measured spatial profiles versus time, temperature, and layer number (abstract and results/discussion sections)."},{"response":"We have added a quantitative comparison in the revised discussion and supplementary information showing that the measured speeds and isotropy exceed typical phonon-assisted or defect-limited diffusion constants reported for similar van der Waals semiconductors by more than an order of magnitude. The unique enhancement precisely at the Néel temperature is difficult to reconcile with phonon drag or static defects, which lack this magnetic-phase-specific signature. While we agree that isotopic substitution or controlled defect studies would be ideal, such experiments are not part of the present dataset; we have noted this limitation and the rationale for the magnon-drag assignment based on the existing temperature and dimensionality dependence.","revision_made":"partial","referee_comment":"[Results and Discussion] Alternative mechanisms (phonon drag, defect trapping, or conventional diffusion) are invoked as insufficient but are not quantitatively compared or experimentally excluded; targeted controls such as magnetic-field dependence, isotopic substitution, or defect-density variation would be required to make the magnon-drag assignment load-bearing (results and discussion sections)."},{"response":"We thank the referee for highlighting this presentational issue. In the revised manuscript we have included error bars on all temperature-dependent propagation data (derived from repeated measurements on multiple samples), detailed the Gaussian fitting procedure used to extract cloud widths and velocities, and added a statistical analysis (including confidence intervals) confirming that the enhancement near the Néel temperature is significant. These updates appear in the main figures, methods section, and a new supplementary note on data analysis.","revision_made":"yes","referee_comment":"[Experimental Results] The temperature-dependent enhancement at the Néel temperature and the reported propagation speeds are presented without quantitative error bars, fitting details, or statistical analysis of the time-resolved maps, which weakens the claim that the behavior is substantially enhanced and distinct from conventional mechanisms (experimental data presentation)."}],"tokens_in":1463,"tokens_out":707,"duration_ms":65926,"standing_objections":[]},"desk_editor":{"model":"grok-4.3","letter":"The main point is that this work reports new experimental signatures of exciton motion in the antiferromagnet CrSBr: ultrafast nearly isotropic propagation that strengthens near the Neel temperature, transient cloud contraction and expansion at low temperatures, and superdiffusive behavior in bilayers. The authors attribute these to drag forces from laser-induced incoherent magnons rather than ordinary diffusion or phonon effects.","headline":"Exciton transport in CrSBr shows temperature-enhanced isotropic spreading and low-T anomalies that the authors link to magnon drag, but the paper lacks any quantitative model or estimate to support that mechanism.","tokens_in":2376,"tokens_out":160,"would_cite":false,"duration_ms":38578,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":{"model":"grok-4.3","evidence":[{"relation":"unclear","rs_module":"IndisputableMonolith/Cost/FunctionalEquation.lean","rs_theorem":"washburn_uniqueness_aczel","paper_passage":"We propose that the drag forces exerted by these currents can effectively imprint characteristic properties of spin excitations onto the motion of excitons."},{"relation":"unclear","rs_module":"IndisputableMonolith/Foundation/ArithmeticFromLogic.lean","rs_theorem":"embed_injective","paper_passage":"Our theoretical analysis in Section S7 demonstrates that the underlying interaction is distinct from the exciton-magnon coupling recently observed in the canted spin state."}],"headline":"Standard magnon-drag transport model in CrSBr with no RS cost or ratio structure","alignment":"orthogonal","rationale":"The paper's machinery consists of drift-diffusion equations, magnon dispersion calculations (including dipole-dipole terms), and phenomenological exciton-magnon scattering rates to explain observed D*, contraction, and superdiffusion. These are conventional condensed-matter constructs with adjustable parameters (scattering times, fluences, temperatures) and make no reference to J-cost, cosh identities, φ-ladder spacings, 8-tick periodicity, or parameter-free derivations. RS has no opinion on this specific mesoscopic transport phenomenology.","tokens_in":62040,"confidence":"moderate","tokens_out":306,"duration_ms":17930,"cache_read_input_tokens":38528,"cache_creation_input_tokens":0},"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"grok-4.3","headline":"In CrSBr, laser-induced magnon currents exert drag forces that transport excitons ultrafast and nearly isotropically.","keywords":["exciton transport","magnon currents","antiferromagnet","CrSBr","van der Waals semiconductor","spin excitations","drag forces"],"falsifier":"Exciton transport that shows no enhancement exactly at the Neel temperature, or that remains unchanged when an external magnetic field alters the magnon spectrum, would falsify the proposed magnon-drag mechanism.","tokens_in":2668,"feed_emoji":"🧲","tokens_out":472,"duration_ms":38088,"temperature":0.7,"pith_summary":"The paper establishes that excitons in the antiferromagnetic van der Waals semiconductor CrSBr show ultrafast, nearly isotropic propagation that strengthens markedly at the Neel temperature, plus transient contraction and expansion of exciton clouds at low temperatures and superdiffusive spreading in bilayers. These behaviors do not match conventional diffusion, phonon hopping or defect-driven motion. The authors instead tie the signatures to currents of incoherent magnons generated by the laser pulse, which scatter with excitons and produce drag forces. This scattering imprints spin-excitation properties directly onto exciton trajectories. A reader would care because the mechanism suggests a route to steer optical energy and information using magnetic degrees of freedom in layered materials.","feed_headline":"Magnon currents drive exciton transport in CrSBr","feed_subtitle":"Laser-created spin excitations drag excitons, producing ultrafast isotropic spread enhanced at the Neel temperature.","key_machinery":"Drag forces generated by currents of incoherent magnons through exciton-magnon scattering.","core_discovery":"The central claim is that the observed ultrafast nearly isotropic exciton propagation, its enhancement at the Neel temperature, the transient contraction and expansion of exciton clouds at low temperatures, and superdiffusive behavior in bilayers arise from drag forces exerted by laser-induced currents of incoherent magnons; exciton-magnon scattering imprints the characteristic properties of these spin excitations onto the motion of the excitons.","pith_inferences":[],"forward_implications":[],"fun_headline_variants":["Magnon currents drag excitons in CrSBr","Spin excitations move excitons ultrafast","Exciton transport via magnons in antiferromagnet","CrSBr shows magnon drag on exciton clouds","Magnon currents enhance exciton spread"],"cache_read_input_tokens":2112,"weakest_assumption_plain":"The measured spatial and temporal profiles of exciton emission are shaped primarily by magnon-drag forces rather than by ordinary exciton diffusion, phonon-assisted hopping, or sample defects.","fun_headline_variants_meta":{"raw":{"variants":["Magnon currents drag excitons in CrSBr","Spin excitations move excitons ultrafast","Exciton transport via magnons in antiferromagnet","CrSBr shows magnon drag on exciton clouds","Magnon currents enhance exciton spread"]},"model":"grok-4.3","cost_usd":0.005404,"raw_usage":{"total_tokens":2516,"prompt_tokens":655,"num_sources_used":0,"completion_tokens":67,"cost_in_usd_ticks":54040500,"prompt_tokens_details":{"text_tokens":655,"audio_tokens":0,"image_tokens":0,"cached_tokens":64},"completion_tokens_details":{"audio_tokens":0,"reasoning_tokens":1794,"accepted_prediction_tokens":0,"rejected_prediction_tokens":0}},"tokens_in":655,"tokens_out":67,"duration_ms":30878,"temperature":1.0,"reasoning_tokens":1794,"cache_read_input_tokens":64,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-05-19T05:40:02.549037+00:00","model_set":{"reader":"grok-4.3"},"falsifier":"Exciton transport that shows no enhancement exactly at the Neel temperature, or that remains unchanged when an external magnetic field alters the magnon spectrum, would falsify the proposed magnon-drag mechanism.","supporting_citations":[],"review_version":1}