{"id":"1bc80341-ae52-4794-953b-de0c39ffb98a","arxiv_id":"2607.20344","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":5,"one_line_summary":"Temperature-dependent dielectric functions of ternary MoSSe and WSSe are extracted over 80–670 K and show Varshni-type shifts of excitonic peaks, enabling simulated thermo-tunable ultra-thin NIR lenses.","lead":"This paper measures how the optical properties of two ternary transition metal dichalcogenides (MoSSe and WSSe) change with temperature from 80 K to 670 K. The results enable design of ultra-thin lenses whose focal length can be tuned by heating or cooling.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Varshni behavior is imposed by the fitting model, not independently demonstrated; NIR refractive-index tuning and lens focal-length shifts rest on extrapolation beyond the measured 830 nm range.","rationale":"The reader's weakest assumption correctly identifies the central vulnerability: the temperature-dependent dielectric functions are extracted using a model that assumes the persistence of the same Tauc–Lorentz oscillators and forces their energies and widths to follow Varshni and Bose–Einstein forms. Because these forms are imposed, the resulting 'Varshni behavior' is not an independent confirmation of the physics; it is baked into the fitting procedure. The manuscript provides no unconstrained peak-position analysis, no model comparison, and no uncertainty quantification. In addition, the NIR properties that drive the applied claims (refractive-index tunability at 1000 nm, focal-length shift) are explicitly based on extrapolation beyond the measured 430–830 nm range, as stated in Methods. This does not make the paper valueless — the room-temperature ellipsometric data and the temperature-dependent DRC maps are useful experimental contributions, and the parent-binary comparison helps validate the RT optical constants. But the headline claim that temperature evolution is 'governed by Varshni's formalism' is currently a modeling assumption rather than a demonstrated finding. The proposed test — refitting with free oscillator parameters at each temperature and comparing to the constrained fits — would settle whether the Varshni/BE forms are actually consistent with the data or simply imposed. Since the reader already flagged this and assigned CONDITIONAL, no verdict change is needed; the concern remains open pending that check.","tokens_in":11131,"tokens_out":3127,"duration_ms":27425,"concrete_test":"Re-fit the 24 temperature-dependent DRC spectra with the same Tauc–Lorentz model but with oscillator energies Eo(T) and broadenings Γ(T) as free parameters at each temperature, using the room-temperature ellipsometric parameters only as initial guesses and imposing no Varshni or Bose–Einstein constraints. Compare the free-fit Eo(T) and Γ(T) values against the Varshni/BE curves reported in Fig. 3 and Tables S5–S6. If the free-fit values agree within confidence intervals, the claim is supported; if they deviate systematically or exhibit large scatter, the reported Varshni behavior is an artifact of the imposed functional forms. As a secondary check, compute the in-plane refractive index at 1000 nm from the free-fit parameters and compare it with the extrapolated values; a significant discrepancy would undermine the lens focal-length predictions.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's central claim — that the temperature evolution of the dielectric responses of ternary MoSSe and WSSe is governed by Varshni's formalism, and that this drives the reported NIR refractive-index tunability and lens focal-length shift — is not independently established. In the temperature-dependent analysis, the DRC spectra are fit using Tauc–Lorentz oscillators whose energies are constrained to follow Varshni's relation and whose broadenings follow the Bose–Einstein phonon form (Results; Methods). The extracted Eo(T) and Γ(T) therefore necessarily reproduce those functional forms, making the 'Varshni behavior' a property of the model rather than a finding from the data. The DRC maps directly show only that existing critical points shift with temperature; they do not reveal the functional form of that shift. Furthermore, the NIR values at 1000 nm — including the lossless refractive index changes and the lens focal-length shift from 835.4 µm at 80 K to 773 µm at 670 K — are extrapolated from fits to 430–830 nm reflectance data (Methods: 'extrapolated up to 1000 nm from 830 nm using the fitted model parameters'). No error bars are provided, and no experimental lens verification is reported. If the imposed oscillator model is not exact, the quantitative device predictions and the claim of Varshni-governed dispersion could be artifacts of the fit.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports room-temperature (RT) in-plane and out-of-plane dielectric functions of ternary MoSSe and WSSe, benchmarked against parent binary TMDs using spectroscopic micro-ellipsometry over 360–1000 nm. It then uses temperature-dependent micro-reflectance differential reflectance contrast (DRC) over 430–830 nm and 80–670 K, analysed with Tauc–Lorentz oscillators whose energies are constrained to Varshni's relation and widths to a Bose–Einstein broadening model, to extract temperature-dependent dielectric functions. From these it claims that the temperature evolution of the Vis dielectric response is 'governed by Varshni's formalism,' that the NIR lossless refractive index is thermally tunable (e.g., n 4.069→4.282 for WSSe at 1000 nm), and that a WSSe plano-convex ultrathin lens shows a focal-length shift from 835.4 µm at 80 K to 773 µm at 670 K.","tokens_in":11524,"tokens_out":5240,"duration_ms":47523,"significance":"If the reported temperature-dependent optical constants are reliable, the dataset would be a useful reference for ternary TMDs over a wide temperature range, and the lens demonstration would illustrate a route to thermo-driven ultrathin photonics. The room-temperature ellipsometry appears well validated by comparison with parent compounds and by micro-reflectance agreement. However, the Varshni-governed claim is currently an input to, not an output of, the fitting model, and the quantitative NIR and lens predictions rest on an extrapolation beyond the measured spectral range without uncertainties. These issues must be resolved before the central claims can be accepted.","major_comments":[{"comment":"The central claim that the temperature evolution is 'governed by Varshni's formalism' is circular. The authors state that 'the oscillator energies were described by Varshni's relation' before fitting, and the extracted Eo(T) in Fig. 3(c,d,g,h) therefore reproduce the imposed form. The DRC maps in Fig. 2 directly demonstrate only that the critical points shift monotonically with temperature; they do not establish a Varshni functional form. The claim should be reworded as a modelling assumption, or the paper should include a test of alternative forms (e.g., unconstrained fits of Eo(T) at each temperature, or comparison with Bose–Einstein or O'Donnell–Chen gap expressions) and report residuals.","section":"Results: 'The temperature dependence of dielectric functions of ternary TMDs'"},{"comment":"The 1000 nm values—including the reported refractive-index changes and the lens focal-length shift—are not measured. Methods states that the dielectric functions were 'extrapolated up to 1000 nm from 830 nm using the fitted model parameters.' The temperature-dependent DRC data span 430–830 nm. Thus the claims of lossless NIR tunability and the 925 nm lens performance are model extrapolations. Please label them as such throughout, and ideally validate with temperature-dependent measurements extending into the NIR or provide a sensitivity analysis of the extrapolation.","section":"Methods: 'Temperature dependent micro-reflectance spectroscopy'"},{"comment":"No uncertainties are reported for any extracted parameter. The temperature-dependent extraction is a multi-oscillator simultaneous fit with many free parameters (amplitudes, Varshni coefficients, broadening parameters, ε∞, and a high-energy tail correction), and strong correlations are likely. Without confidence intervals or a residual analysis, the quantitative claims—e.g., WSSe focal length from 835.4 µm to 773 µm, Δn at 1000 nm—cannot be evaluated. Add error bars, bootstrapped confidence regions, or at least a covariance matrix for the fit parameters.","section":"Results and Methods: temperature-dependent fitting"},{"comment":"The extraction assumes that no new optical transitions appear down to 80 K and that the oscillator set is identical to the room-temperature model. This assumption is stated as a conclusion ('suggesting main effect to be governed by modification of Tauc–Lorentz oscillator parameters rather than the emergence of new optical transitions'). If new transitions or changes in oscillator strengths/line shapes occur, the imposed Varshni parameters would absorb them. The paper should test the assumption, e.g., by fitting each temperature independently and comparing residuals, or by including an additional oscillator and showing it is not required.","section":"Results: 'The temperature dependence of dielectric functions of ternary TMDs'"}],"minor_comments":[{"comment":"The caption says dashed curves represent out-of-plane components 'Re[εz] and Im[εxy]'; the second should presumably be Im[εz].","section":"Fig. 1 caption"},{"comment":"The phrase 'across 430-1000 nm spectral region' is ambiguous. Room-temperature ellipsometry covers 360–1000 nm, but temperature-dependent DRC covers 430–830 nm and the NIR part is extrapolated. Please state this distinction explicitly in the abstract and main text.","section":"Abstract and Results"},{"comment":"The phrase 'infirmly absorbing' should be 'weakly absorbing'.","section":"Results: lens section"},{"comment":"In Eq. (3), N is not defined. Specify that it is the number of Tauc–Lorentz oscillators used in the fit.","section":"Methods: 'Room temperature spectroscopic micro-ellipsometry'"},{"comment":"The term 'super-mossian characteristics' is used without definition or context; a brief explanation or reference would help the reader.","section":"Introduction"}],"recommendation":"major_revision","confidential_remarks":"The main issue is circularity, not lack of experimental effort; the room-temperature ellipsometry appears carefully validated. If the authors reframe the Varshni claim as a modelling assumption, clearly label the NIR extrapolation, and add uncertainty quantification, the paper could be publishable. I would not require new NIR measurements for publication if the extrapolation is clearly caveated, though they would substantially strengthen the device claims."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague, here is my read of arXiv:2607.20344. The useful thing is the dataset: first temperature-dependent dielectric functions for ternary MoSSe and WSSe from 80 to 670 K, with room-temperature ellipsometry that reproduces the parent binaries well. The hybrid approach—using ellipsometry to anchor the model and reflectance contrast to track temperature—is sensible and likely to be reused.\n\nSoft spot is the headline claim. The text says temperature evolution is governed by Varshni's formalism, but the oscillator energies are constrained to Varshni's relation before fitting. So the extracted Eo(T) necessarily follows that curve. Same for Bose-Einstein broadening. The DRC maps show the critical points shift with temperature, but they don't reveal the functional form. If the authors had fit Eo(T) freely and then compared to Varshni, the claim would be a result. As written, it's an assumption. That doesn't make the data worthless, but it changes the framing from 'discovery' to 'model parameterization.'\n\nAlso: no error bars on any of the extracted dielectric functions, and the 1000 nm values—including the refractive index tunability and focal length shift—are extrapolated from 830 nm using the fitted model. The lens is a design calculation, not an experiment. So the quantitative device predictions are conditional on the model being correct.\n\nStill, I think this deserves a serious referee. The dataset itself is new and useful for anyone designing thermo-tunable TMD photonics. A referee should ask for unconstrained peak positions, uncertainty propagation, and a more careful wording of the Varshni claim. The paper is honest in its methods; it just oversells the physical conclusion.\n\nRecommendation: send to review, with requests to address the circularity and extrapolation.","headline":"Useful first dataset for temperature-dependent optical constants of ternary MoSSe and WSSe, but the central 'Varshni governs' claim is built into the fitting model and the headline NIR numbers are extrapolated beyond the measured range.","tokens_in":11980,"tokens_out":1918,"would_cite":true,"duration_ms":16882,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["78.20.Ci"],"model":"deepseek-v4-flash","headline":"Ternary TMDs tune their refractive index with temperature from 80 to 670 K","keywords":["ternary TMD","dielectric permittivity","temperature dependence","Varshni relation","refractive index","ultrathin lens","MoSSe","WSSe"],"falsifier":"Direct spectroscopic ellipsometry on WSSe or MoSSe at 925–1000 nm from 80 to 670 K: if the refractive index does not increase by the predicted ~0.2 (or if absorption emerges), the extrapolated dielectric functions and the lens focal-length shift would be wrong. Additionally, detecting an unexpected new excitonic peak below 80 K would invalidate the fixed-oscillator model and the Varshni claim.","tokens_in":11068,"feed_emoji":"🔬","tokens_out":3817,"duration_ms":38516,"temperature":0.7,"pith_summary":"The paper measures how the dielectric functions of the ternary transition metal dichalcogenides MoSSe and WSSe change across a wide temperature window, from 80 to 670 K, over 430–1000 nm. It claims that the temperature evolution of these dielectric responses is governed by Varshni's relation in the visible range, which blue-shifts excitonic resonances at low temperatures and red-shifts them at high temperatures. Because of Kramers–Kronig consistency, this shift also raises the real part of the dielectric function in the lossless near-infrared tail, increasing the in-plane refractive index by roughly 0.2 units. The authors exploit this using WSSe's measured dispersion to design a 16-layer plano-convex lens whose focal length continuously shifts from 835 µm at 80 K to 773 µm at 670 K, establishing a route to thermo-driven ultrathin photonic components without moving parts.","feed_headline":"Ternary TMDs tune their refractive index from 80 to 670 K","feed_subtitle":"A 16-layer WSSe lens shifts its focus by 62 µm as temperature swings from 80 to 670 K.","key_machinery":"The key machinery is the Tauc–Lorentz oscillator parameterization of the in-plane dielectric function, whose energy and broadening parameters are forced to follow Varshni's relation and Bose–Einstein phonon broadening. This single parametrized model, seeded with room-temperature spectroscopic ellipsometry data, is fitted simultaneously to temperature-dependent differential reflectance spectra over 430–830 nm and then extrapolated to 1000 nm. It is what turns sparse reflectance maps into a continuous temperature-dependent dielectric function dataset, and it is the same dataset that drives the lens focal-length calculations.","core_discovery":"The central discovery is that the temperature-dependent optical response of ternary TMDs in the visible is fully captured by Varshni's formalism: each excitonic oscillator's energy follows E(T)=E(0)−αT²/(β+T) and its broadening follows Bose–Einstein phonon statistics, with no new optical transitions appearing down to 80 K. As a direct consequence, the transparency edge redshifts with heating, which, through Kramers–Kronig relations, monotonically increases the refractive index in the extinctionless NIR tail (e.g., for WSSe, n rises from 4.069 to 4.282 at 1000 nm; for MoSSe, from 4.259 to 4.561). The authors demonstrate the practical potential by designing a suspended ultra-thin WSSe lens tha","pith_inferences":["Because the Varshni functional form is imposed in the fit, the reported 'Varshni behavior' is partly an artifact of the model choice; a direct, fit-independent measurement of exciton energies (e.g., photoluminescence peaks) would strengthen the conclusion.","The NIR behavior beyond 830 nm was not directly measured but extrapolated from the fitted model to 1000 nm; direct ellipsometry or transmittance measurements at a few temperatures in the 900–1000 nm window would verify the lossless tunability claim.","The same temperature-resolved dielectric dataset could be used to design thermally tunable metasurfaces, waveplates, or absorption modulators in the NIR, not just lenses, potentially enabling reconfigurable flat optics without mechanical motion.","The excitonic blue-shift with cooling may be partly due to lattice contraction rather than pure electron-phonon interaction; disentangling these contributions would make the physical model more transferable to other TMD systems."],"forward_implications":["The dielectric permittivity of MoSSe and WSSe obeys Varshni's relation across the full 80–670 K temperature window.","The in-plane refractive index in the lossless NIR tail increases monotonically with temperature, providing a ~0.2 tunable index swing at 1000 nm.","A suspended 16-layer WSSe plano-convex lens shows a continuous focal-length shift from 835.4 µm at 80 K to 773 µm at 670 K.","The hybrid ellipsometry-plus-microreflectance approach can be extended to a broader class of van der Waals crystals, including biaxial ones.","Excitonic A and B states remain the most robust optical transitions across the temperature range, while higher-energy states show stronger broadening, indicating stronger electron–phonon coupling."],"fun_headline_variants":["Heating shifts TMD lens focus by 62 µm","Ternary TMD refractive index rises with temperature","80–670 K: Ternary TMDs tune refractive index","Temperature-controlled TMD lens shifts focus 62 µm","Varshni formalism explains TMD optics from 80 to 670 K"],"cache_read_input_tokens":2304,"weakest_assumption_plain":"The entire temperature dependence is captured by a fixed set of Tauc–Lorentz oscillators whose energies and widths are forced to follow Varshni and Bose–Einstein formulas; if new optical transitions appear below 80 K, or if these functional forms are incorrect, the reported Varshni behavior and refractive-index changes are artifacts of the fit.","fun_headline_variants_meta":{"raw":{"variants":["Heating shifts TMD lens focus by 62 µm","Ternary TMD refractive index rises with temperature","80–670 K: Ternary TMDs tune refractive index","Temperature-controlled TMD lens shifts focus 62 µm","Varshni formalism explains TMD optics from 80 to 670 K"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000193,"raw_usage":{"total_tokens":1196,"prompt_tokens":763,"completion_tokens":433,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":507,"completion_tokens_details":{"reasoning_tokens":351}},"tokens_in":507,"tokens_out":433,"duration_ms":4536,"temperature":1.0,"reasoning_tokens":351,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-01T10:04:42.175811+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Direct spectroscopic ellipsometry on WSSe or MoSSe at 925–1000 nm from 80 to 670 K: if the refractive index does not increase by the predicted ~0.2 (or if absorption emerges), the extrapolated dielectric functions and the lens focal-length shift would be wrong. Additionally, detecting an unexpected new excitonic peak below 80 K would invalidate the fixed-oscillator model and the Varshni claim.","supporting_citations":[],"review_version":1}