{"id":"b80302b7-ec1f-44ce-ae75-79638489027e","arxiv_id":"2506.01259","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"Polaritons in a MoSe2 monolayer coupled to a 2D photonic crystal propagate about 20 micrometers, one order of magnitude farther than bare excitons, with transport controlled by band structure and pump power.","lead":"This paper reports that polaritons, hybrid light-matter particles formed by coupling excitons in a monolayer semiconductor to photonic crystal modes, travel tens of microns, about ten times farther than bare excitons. The transport distance can be tuned by changing the photonic crystal design and the laser power, which could enable integrated on-chip polariton devices.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Reported 20-um transport length may be a finite-size boundary artifact: the exponential fits are made between the pump and a bright PhC edge whose distance is itself ~20 um.","rationale":"The paper has real strengths: a uniform dodecanol-encapsulated monolayer over an array of PhCs with different periods, measured ~35 meV vacuum Rabi splitting, momentum-resolved dispersion, and extension to other TMDs and room temperature. The reader's conditional verdict is balanced. In my stress pass, the weakest load-bearing point is not the assignment of the distant low-energy emission to the lower polariton branch, but the way the transport length itself is defined and measured. The fits in Fig. 3(c) run from the pump to a strongly emitting boundary, and the fitted values in Fig. 3(d) saturate at ~20 um for all energies above threshold. With device widths of 15–30 um, a bright edge at 15–20 um can force an exponential fit to a 'length' comparable to the edge distance even when the underlying polariton mean free path is much shorter. The absence of width controls and error bars means the order-of-magnitude claim is not yet secured. The proposed width/pump-position or time-resolved test would settle this directly without requiring new physics assumptions. If it passes, the paper's central claim is strongly supported; if it fails, the claim would need to be reframed as edge-mediated photon/polariton scattering rather than intrinsic long-range transport. I therefore keep the reader's CONDITIONAL verdict, with the additional explicit condition of a boundary/finite-size control.","tokens_in":9294,"tokens_out":7689,"duration_ms":94984,"concrete_test":"Perform the same PL imaging and exponential-fit analysis on PhC devices with the same lattice and period but with at least three different widths (e.g., 10, 20, and 40 um), or repeat a given device with the pump positioned at different distances from the boundary, keeping pump power and photon energy fixed. If the fitted transport length scales with device width or with pump-to-boundary distance, or remains pinned near the boundary position rather than changing with dispersion, the reported ~20 um is a geometric artifact. An independent check is time-resolved PL with the field of view extended beyond the device: an intrinsic polariton propagation length would produce a time-of-flight or decaying spatial profile that is independent of edges.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The quantitative central claim — 'transport length over an order of magnitude longer than bare excitons' — is extracted in Fig. 3(c) from single-exponential fits of steady-state PL profiles over the interval X = 0 (pump) to X = B (photonic-crystal boundary). The very same data show strong emission at the boundary (Fig. 2(g); Fig. 3(a,c)), and Fig. 3(d) shows all fitted transport lengths saturating at ~20 um above threshold. Since the fabricated PhCs are 15–30 um wide, the fitted length is degenerate with the pump-to-boundary distance: a profile that is bright at the pump and bright at the edge can be represented by a ~20 um exponential regardless of the intrinsic polariton propagation length. No control on device width, no pump-position scan, and no error bars are reported. Thus the headline order-of-magnitude enhancement and the threshold-like jump could be finite-size/boundary-scattering artifacts rather than evidence of long-range polariton transport. This concern is independent of, and more load-bearing than, the spectral-origin question raised in the reader's verdict: even if the distant emission is entirely from the lower polariton branch, the extracted length scale may measure the device geometry.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports photoluminescence imaging of a dodecanol-encapsulated MoSe2 monolayer placed on suspended 2D silicon nitride photonic crystals. Under non-resonant excitation, the PL spreads over tens of micrometers across the PhC, whereas on a flat substrate it remains within 1-2 μm. Momentum-resolved reflection contrast and PL spectra show strong coupling with vacuum Rabi splitting near 35 meV. The authors compare three PhCs with different lattice constants, observe different transport lengths that they correlate with polariton group velocity and relaxation, and report a threshold-like jump in transport length with pump power, which they attribute to bosonic stimulated relaxation.","tokens_in":9457,"tokens_out":8312,"duration_ms":85325,"significance":"If the transport is truly polaritonic, this would be a substantial advance: it would demonstrate the first long-range and designable polariton transport in 2D photonic-crystal slabs, overcoming the limitations of vertical cavities and waveguides. The experimental platform is strong—large-area encapsulated monolayer, systematic lattice-constant series, and direct PL imaging. The main weakness is that the quantitative transport length is extracted from single-exponential fits over a finite interval that ends at a bright boundary, and the spectral identity of the distant emission is not fully established. These two issues directly affect the headline claims of 'order-of-magnitude enhancement' and 'stimulated relaxation', and need to be addressed with additional control experiments.","major_comments":[{"comment":"The transport lengths in Fig. 3(d) are obtained from single-exponential fits to the PL profiles between X=0 (pump) and X=B (PhC boundary), as shown in Fig. 3(c). The PhC width is 15–30 μm (stated in the first paragraph of Results), and the profiles exhibit a pronounced intensity maximum at the boundary, explicitly described in the text as 'strong emission at the boundary due to enhanced scattering.' For a profile that is bright at both the pump and the boundary, a single-exponential fit over the interval [0, B] will return a decay length of order B irrespective of the intrinsic propagation mechanism. The saturation of all fitted L values near 20 μm above threshold in Fig. 3(d) is consistent with this geometric artifact. No controls are reported: no devices with different widths, no scans of the pump position relative to the boundary, no error bars on L, and no fit residuals or goodness-of-fit metrics. Until such controls are provided, the order-of-magnitude enhancement and the threshold-like jumps cannot be distinguished from finite-size and boundary-scattering effects.","section":"Fig. 3(c)-(d) and Section 'Pump power dependence'"},{"comment":"The assignment of the distant PL to lower-branch polaritons is not fully supported. Momentum-resolved spectra (Figs. 1(e), 2(d-f)) show strong coupling at or near the excitation spot, but the manuscript does not show that the emission at the boundary (X=B) has the same polariton dispersion. The redshifted spectra at the boundary (Fig. 3(b), right) could alternatively arise from uncoupled photonic slab modes guided to the boundary and scattered out, from defect states, or from reabsorption and re-emission by excitons. Furthermore, the reference measurement is on a flat substrate, which does not control for the photonic environment alone; a PhC with the exciton uncoupled (e.g., large detuning) would be needed to confirm that the enhanced transport requires polariton formation. The authors should provide a spatially resolved spectrum at the boundary overlaid with the calculated polariton band structure, and include an uncoupled control.","section":"Spectral origin and control (Figs. 1(d-e), 2(g), 3(a-c))"},{"comment":"The claim of stimulated relaxation rests on the threshold-like increase in transport length and emission redshift in Fig. 3(d). Because the transport length values are confounded by the boundary artifact described above, the threshold behavior is not yet established. In addition, the thresholds are inferred from a small number of data points without error bars or a statistical fit; the authors should present a quantitative analysis (e.g., a bilinear fit with confidence intervals) and preferably an independent signature of stimulated scattering, such as a nonlinear increase in emission intensity or a reduction in linewidth, in order to support the 'stimulated relaxation' conclusion.","section":"Stimulated relaxation (Fig. 3(d))"}],"minor_comments":[{"comment":"In the Methods section, 'LPhCVD' appears to be a typo for 'LPCVD'.","section":"Methods"},{"comment":"The statement 'The total width of each PhC varies between 15−30μm' should clarify whether this width refers to the dimension along the measured transport direction.","section":"Results, first paragraph"},{"comment":"Fig. 2(g) caption and the text use different integration windows (1.640–1.655 eV in Fig. 2(g), versus 1.64, 1.60, and 1.55 eV in Fig. 3(c)); please define the integration window for each profile in the figure captions and text.","section":"Figures 2 and 3"},{"comment":"The symbol 'P' is used both for the pump power and for the label of the PhC spot (Spot P); please disambiguate.","section":"Throughout"},{"comment":"The statement that the phenomena extend to MoS2, WSe2, and WS2 and to room temperature is only mentioned in the text with reference to supplementary figures; it would strengthen the paper to give a brief summary of those results in the main text.","section":"Results, final paragraph"}],"recommendation":"major_revision","confidential_remarks":"The skeptic's boundary-artifact concern is serious and should be addressed with additional experiments before publication. In particular, the authors should perform a scan of the pump position relative to the boundary or fabricate devices with varying width and show that the fitted decay length scales accordingly, or provide time-resolved imaging that directly shows propagation. The current manuscript does not yet provide the evidence needed to distinguish polariton transport from photon scattering at the boundary."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Quick take: this is the first transport study of TMD exciton-polaritons in a slab 2D photonic crystal, and the qualitative result—PL spreads tens of microns on the PhC and not on flat substrate—is probably real. But the quantitative \"20 um transport length\" is not yet established. The fits are made between the pump and a bright PhC boundary on devices only 15-30 um wide, and no width series, pump-position scan, or error bars are shown. That is exactly the configuration where a fitted exponential decay length can just mirror the pump-to-edge distance.\n\nWhat is actually new: previous TMD-PhC work showed strong coupling and polariton bands; this paper adds spatially resolved transport and a systematic comparison across three lattice constants on one continuous monolayer. The large-area dodecanol-encapsulated MoSe2 over an array of PhCs is a genuinely nice experimental design. The momentum-resolved RC spectra with ~35 meV Rabi splitting support the polariton assignment, and the contrast with the flat-substrate PL is visible in the raw images. Credit is due for that.\n\nSoft spots. The boundary-artifact problem is the load-bearing one. A profile that is bright at the pump and bright again at the edge can be represented by a ~20 um exponential no matter how far the polaritons actually propagate. The authors need at least two device widths or a pump-position scan before the order-of-magnitude claim holds. Second, the flat-substrate comparison lacks a control for the suspended, patterned membrane itself; uncoupled photonic slab modes or defect states could contribute to the distant emission. The spectral redshift and momentum dispersion make that less likely, but they do not rule it out. Third, \"stimulated relaxation\" is inferred from a threshold-like jump in transport length and redshift. Heating, state-filling, or simply the onset of edge emission can all produce similar thresholds. That conclusion is more speculative than the data support.\n\nWho should read it: people working on 2D polaritonics and integrated polariton circuits will want to know this system exists and can be tuned. It deserves a serious referee. My recommendation: send it to review, but with a request for the control experiments above before the quantitative transport length and stimulated-relaxation claims are accepted.","headline":"First transport study of TMD polaritons in a slab 2D photonic crystal, with a nice experimental platform, but the headline 20-um transport length may be a boundary artifact and needs control experiments before the quantitative claim can be trusted.","tokens_in":10067,"tokens_out":3866,"would_cite":false,"duration_ms":44164,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["71.36.+c","42.70.Qs"],"model":"deepseek-v4-flash","headline":"Polaritons in a 2D photonic crystal move energy an order of magnitude farther than bare excitons.","keywords":["exciton-polaritons","photonic crystals","2D materials","MoSe2","polariton transport","stimulated relaxation","strong coupling","polariton dispersion"],"falsifier":"Measure the momentum-resolved photoluminescence spectrum at a detection point about 10 μm from the pump: propagating lower polaritons should show a parabolic dispersion matching the designed photonic crystal band structure, whereas reabsorbed and re-emitted excitons would appear dispersionless at the exciton and trion energies. A companion check is time-resolved detection, which should show the far-field signal arriving with a delay consistent with the lower polariton group velocity rather than with the slower exciton diffusion or re-emission timescale.","tokens_in":9038,"feed_emoji":"🔆","tokens_out":9300,"duration_ms":95791,"temperature":0.7,"pith_summary":"The paper reports that coupling excitons in a monolayer semiconductor to the Bloch modes of a 2D slab photonic crystal creates polaritons that travel roughly 20 micrometers, about ten times farther than bare excitons on a flat substrate. The resulting transport length is not fixed: scaling the photonic crystal lattice constant changes the polariton dispersion, and changing pump power shifts the population into faster, lower-energy polariton states, so transport can be designed and tuned. A sharp, threshold-like jump in transport length with increasing power is attributed to bosonic stimulated relaxation, which the authors connect to the possibility of superfluid-like frictionless transport. If correct, this turns a 2D photonic crystal into a chip-integrated platform for controlling energy transport in two-dimensional semiconductors.","feed_headline":"Polaritons push 2D semiconductor transport ten times farther","feed_subtitle":"Coupling excitons to photonic-crystal modes extends transport to ~20 microns and makes it tunable by lattice design.","key_machinery":"The central object is the 2D photonic crystal polariton, a mixed exciton-photon quasiparticle formed by strong coupling between MoSe2 excitons and the Bloch modes of a suspended Si3N4 honeycomb slab photonic crystal. The photonic crystal provides tunable lower polariton dispersions with positive, flat, or negative effective mass depending on the lattice constant, giving high group velocity to low-energy polariton states. The dodecanol-encapsulated macroscopic monolayer is the enabling material platform because it lets one uniform semiconductor be measured across an array of photonic crystals with different parameters.","core_discovery":"Using a dodecanol-encapsulated monolayer of MoSe2 placed over suspended Si3N4 2D photonic crystals with different lattice constants, the authors demonstrate that photoluminescence spreads across the entire photonic crystal, tens of microns from the pump, and extends more than 100 meV below the exciton energy. Momentum-resolved spectra show the emission follows polariton dispersions with a measured vacuum Rabi splitting around 35 meV. The transport length grows from about 2.6 μm below threshold to about 20 μm above threshold, an order-of-magnitude improvement over bare excitons, with the threshold appearing at different pump powers for different emission energies. The dependence of the transport length on the polariton dispersion curvature and on pump power is interpreted as evidence that enhanced transport is carried by lower polariton states and is boosted by stimulated relaxation.","pith_inferences":["Beyond the paper, a time-resolved measurement at a point roughly 10 μm from the pump would separate genuine polariton propagation from reabsorption and re-emission: the arrival delay should match the lower polariton group velocity, whereas re-emitted exciton light would arrive later and at the exciton energy.","The strong emission observed at the photonic crystal boundary suggests that edges scatter or accumulate polaritons; if that scattering is controllable, boundaries could be used to route energy in the plane.","If the threshold is bosonic stimulated scattering, the same pump-power transition should appear as a superlinear rise in the low-energy polariton population and a drop in the second-order coherence $g^{(2)}$ below 1, a test of the superfluid interpretation.","The demonstrated designability of the polariton dispersion could be combined with topological photonic-crystal band designs to turn long-range transport into edge-protected, backscattering-immune channels."],"forward_implications":["If the central claim holds, on-chip energy transport in monolayer semiconductors can be increased from about 1-2 μm to roughly 20 μm simply by patterning the substrate into a photonic crystal.","Transport length becomes a design parameter: scaling the lattice constant changes the lower polariton dispersion and thereby selects which energy states travel far.","The threshold-like jump in transport length with pump power indicates stimulated bosonic relaxation, so at high densities the polariton population shifts into fast low-energy states, the regime in which polariton condensation and frictionless flow could emerge.","The paper states that similar behavior appears in other TMD materials and at room temperature, which would make the platform usable outside cryogenic laboratory conditions.","Because the enhancement is tied to the photonic band structure, the same platform could combine long transport with other photonic-crystal functionalities such as band-edge localization or engineered disorder."],"supporting_citations":[{"why":"Establishes the coupled exciton-photon mode splitting that defines polariton formation.","marker":"[28]"},{"why":"Shows strong light-matter coupling in two-dimensional atomic crystals, the basis for TMD polaritons.","marker":"[29]"},{"why":"Reports imaging of exciton-polariton transport in MoSe2 waveguides, the planar waveguide baseline of tens-of-micron transport that this work extends to photonic crystals.","marker":"[30]"},{"why":"Documents long-range ballistic transport and trapping of room-temperature exciton polaritons in an atomically thin semiconductor.","marker":"[32]"},{"why":"Demonstrates photonic-crystal exciton-polaritons in monolayer semiconductors, the platform on which this work builds transport experiments.","marker":"[36]"},{"why":"Supplies the macroscopic high-quality TMD monolayer method that lets one material be measured across an array of photonic crystals.","marker":"[40]"}],"fun_headline_variants":["2D polaritons travel 10x farther in photonic crystals","Photonic crystals boost 2D polariton transport by 10x","Tunable polaritons carry energy 10x farther in 2D","20-micron polariton transport in 2D photonic crystals","Polaritons extend 2D transport to 20 microns"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The low-energy photoluminescence seen far from the pump is emitted by propagating lower polariton states, not by uncoupled or weakly coupled photonic slab modes, defect states, or reabsorption and re-emission by excitons; if that assignment fails, the long-range signal could be ordinary light or defect-mediated emission rather than polariton transport.","fun_headline_variants_meta":{"raw":{"variants":["2D polaritons travel 10x farther in photonic crystals","Photonic crystals boost 2D polariton transport by 10x","Tunable polaritons carry energy 10x farther in 2D","20-micron polariton transport in 2D photonic crystals","Polaritons extend 2D transport to 20 microns"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000971,"raw_usage":{"total_tokens":4125,"prompt_tokens":935,"completion_tokens":3190,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":551,"completion_tokens_details":{"reasoning_tokens":3093}},"tokens_in":551,"tokens_out":3190,"duration_ms":18919,"temperature":1.0,"reasoning_tokens":3093,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-07T11:46:14.835655+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the momentum-resolved photoluminescence spectrum at a detection point about 10 μm from the pump: propagating lower polaritons should show a parabolic dispersion matching the designed photonic crystal band structure, whereas reabsorbed and re-emitted excitons would appear dispersionless at the exciton and trion energies. A companion check is time-resolved detection, which should show the far-field signal arriving with a delay consistent with the lower polariton group velocity rather than with the slower exciton diffusion or re-emission timescale.","supporting_citations":[{"cited_title":"Weisbuch, M","cited_arxiv_id":null,"evidence_quote":"Establishes the coupled exciton-photon mode splitting that defines polariton formation."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Shows strong light-matter coupling in two-dimensional atomic crystals, the basis for TMD polaritons."},{"cited_title":"Imaging exciton–polariton transport in MoSe 2 waveguides.Nature Photonics, 11(6):356–360, 2017","cited_arxiv_id":null,"evidence_quote":"Reports imaging of exciton-polariton transport in MoSe2 waveguides, the planar waveguide baseline of tens-of-micron transport that this work extends to photonic crystals."},{"cited_title":"Wurdack, E","cited_arxiv_id":null,"evidence_quote":"Documents long-range ballistic transport and trapping of room-temperature exciton polaritons in an atomically thin semiconductor."},{"cited_title":"Photonic-crystal exciton-polaritons in monolayer semiconductors.Nature Communications, 9(1):713, 2018","cited_arxiv_id":null,"evidence_quote":"Demonstrates photonic-crystal exciton-polaritons in monolayer semiconductors, the platform on which this work builds transport experiments."},{"cited_title":"Macroscopic transition metal dichalcogenides monolayers with uniformly high optical quality.Nature Communications, 14(1):1837, 2023","cited_arxiv_id":null,"evidence_quote":"Supplies the macroscopic high-quality TMD monolayer method that lets one material be measured across an array of photonic crystals."}],"review_version":1}