{"id":"026cb9de-670a-40c5-8399-6ae7fe0ee6e4","arxiv_id":"2412.03935","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":8.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"Time- and polarization-resolved photoemission shows valley-polarized Floquet-Bloch states in 2H-WSe2 under circularly polarized below-gap infrared driving, with theory indicating over 50% valley selectivity in the dressed population.","lead":"Researchers photoexcited tungsten diselenide with circularly polarized infrared light and found that the light-dressed electronic states split by valley, with opposite valleys responding to opposite helicities. The work merges Floquet band engineering with valleytronics and may point to new all-optical control of quantum materials.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The >50% Floquet valley polarization is an inferred decomposition output, not a direct measurement, and the Volkov background that dilutes the measured ~15% asymmetry is set by a Fresnel dielectric model whose sensitivity is shown but not bounded in Extended Data Fig. 10.","rationale":"The reader's weakest-assumption analysis identifies exactly the load-bearing point: the >50% Floquet valley polarization is an inferred quantity, and its inference depends on the dielectric/Fresnel model for the in-sample pump field. I agree with that assessment after reading the full text. The paper has real strengths: the data are openly available, the momentum microscope resolution and fluence are characterized in detail, the detuning scan in Extended Data Fig. 6 provides some independence from a single resonance condition, and the theory separates Floquet-only and Volkov-only contributions clearly. None of these, however, turns the >50% claim into a direct observable. Extended Data Fig. 10 demonstrates that the Volkov contribution changes with epsilon_r, but the paper does not propagate that sensitivity into the headline number or provide error bars on the measured asymmetry. The qualitative demonstration of valley- and polarization-dependent Floquet-Volkov interference is well supported; the quantitative '>50% valley-polarized Floquet-Bloch populations' claim needs either a calibrated field determination or an explicit epsilon_r sensitivity bound. The reader's CONDITIONAL verdict is therefore appropriate, and my stress-test does not move it.","tokens_in":21445,"tokens_out":6234,"duration_ms":61226,"concrete_test":"Use the p-polarized pump data from Extended Data Fig. 2(d)-(f), which the paper identifies as Volkov-dominated, to calibrate the effective in-sample pump field within the Fresnel model. Then recompute the circular-polarization decomposition of Fig. 3(f) with this calibrated field, and also for the range of epsilon_r values used in Extended Data Fig. 10. If the Floquet-only valley polarization at RCP/LCP remains above 50% across the physically plausible epsilon_r range, the dielectric-model concern is non-load-bearing; if it drops below 50% for any plausible value, the quantitative claim must be revised or explicitly qualified.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central quantitative claim, stated in the main text as 'photonic dressing using circularly-polarized light leads to strongly valley-polarized Floquet-Bloch populations, i.e. >50% under our experimental conditions,' is not directly measured. The measured sideband valley asymmetry at RCP/LCP is about ±15% (Fig. 3e); the >50% figure comes from the theoretical decomposition in Fig. 3f that isolates the Floquet-only contribution. That decomposition is controlled by the magnitude of the Volkov background at circular polarization, which in the model is set by the effective in-sample pump field A_pump(t) obtained from a sharp-interface Fresnel model (Methods, Eq. (1) and the surrounding discussion). Extended Data Fig. 10 explicitly shows that the valley-resolved Volkov signal depends on the assumed dielectric constant epsilon_r, so the dilution of the measured asymmetry by Volkov terms, and therefore the extracted Floquet-only polarization, is epsilon_r-dependent. The paper does not report a sensitivity range for the >50% claim, nor error bars on the measured asymmetry. The body also concedes that Volkov-only simulations reproduce most observed features, which makes the 'unambiguous' language in the abstract and conclusions stronger than the evidence supports. The qualitative valley-dependent Floquet-Volkov interference is credible, but the quantitative headline polarization is load-bearing and currently rests on an uncalibrated model parameter.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports time- and polarization-resolved XUV momentum microscopy on 2H-WSe2 driven by 1.2 eV IR pulses, together with td-NEGF simulations, and claims the formation of valley-polarized Floquet-Bloch states. The central observations are a polarization- and valley-dependent modulation of the +ℏω sideband intensity and angular distribution, which the authors attribute to quantum path interference between Floquet-Bloch and Volkov transitions, and an XUV circular dichroism signal from the dressed sideband that indicates VB-CB orbital hybridization. The theoretical modeling is parameterized from DFT and reproduces the qualitative polarization dependence, including a valley asymmetry that flips sign at s-polarization. The main quantitative claim is that circularly polarized driving creates strongly valley-polarized Floquet-Bloch populations, stated as '> 50%' in the main text, extracted by decomposing the total calculated sideband signal into Floquet-only and Volkov-only contributions.","tokens_in":21677,"tokens_out":2162,"duration_ms":22144,"significance":"If the central claim is correct, the paper would be a notable step in Floquet engineering: it would demonstrate valley-selective Floquet-Bloch dressing in a TMDC and connect it to orbital-texture changes visible in XUV CD-ARPES. The strengths of the paper are its integrated experimental-theoretical approach, the use of an external experimental benchmark rather than fitting the valley asymmetry, the inclusion of photoemission matrix elements from first principles, and the open data availability. The qualitative picture of polarization- and valley-dependent Floquet-Volkov interference is credible and is supported by the agreement between the measured and calculated angular distributions near s-polarization. However, the headline quantitative claim of >50% Floquet valley polarization is an inferred decomposition output rather than a directly measured quantity, and the paper does not currently bound the sensitivity of that decomposition to the Fresnel model parameter that controls the Volkov background.","major_comments":[{"comment":"The assertion that circularly polarized driving yields 'strongly valley-polarized Floquet-Bloch populations, i.e. > 50%' is not directly measured. The measured sideband valley asymmetry at RCP/LCP is about ±15% (Fig. 3e), and the >50% figure is obtained by decomposing the calculated signal into Floquet-only and Volkov-only contributions (Fig. 3f). Because the Volkov background is much larger than the Floquet contribution at circular polarization, the extracted Floquet-only polarization is a sensitive function of the model used for the in-sample field. The manuscript should either provide a sensitivity analysis of the >50% figure with respect to the dielectric constant and other model inputs, or clearly restate the claim as a model-dependent inference rather than a measured polarization.","section":"Main text, 'Valley-Polarized Floquet-Bloch States'; Fig. 3(e)-(f)"},{"comment":"The decomposition that isolates the Floquet-only valley asymmetry is controlled by the magnitude of the Volkov contribution, which in the model is set by the effective in-sample pump vector potential A_pump(t) obtained from a sharp-interface Fresnel model. Extended Data Fig. 10 shows that the valley-resolved Volkov signal changes with the assumed dielectric constant ε_r, and the text acknowledges that 'Volkov-only' simulations reproduce most experimental features. No uncertainty range for ε_r, no error bars on the measured asymmetry, and no propagation of these uncertainties into the >50% Floquet polarization are reported. This is a load-bearing gap: without bounding the model dependence, the quantitative headline claim is not established to the standard implied by the abstract's 'unambiguously'.","section":"Methods, Theoretical calculations, Eq. (1) and Fresnel discussion; Extended Data Fig. 10"},{"comment":"The manuscript states that the standard Floquet spectral function is independent of the driving helicity and does not reproduce the valley-polarized Floquet bands, whereas the td-NEGF calculation does. This makes the central valley-polarization claim dependent on the specific td-NEGF treatment rather than on a directly observed helicity asymmetry. The paper should make explicit what physical ingredient in the td-NEGF calculation (beyond standard Floquet theory) produces the helicity-dependent valley polarization, and why that ingredient is not itself an artifact of the finite-pulse model or the assumed broadening/dephasing. Without this, the 'unambiguous demonstration' language in the conclusions is stronger than the evidence presented.","section":"Main text, 'Valley- and Polarization-Resolved Quantum Path Interferences'; Extended Data Figs. 4 and 8"}],"minor_comments":[{"comment":"The experimental valley asymmetry in Fig. 3(e) is shown without statistical or systematic error bars, even though the text quotes a convergence to about ±15%; adding error bars or stating the uncertainty in the caption would help the reader judge the significance of the sign flip and the circular-polarization values.","section":"Fig. 3(e) and related text"},{"comment":"The caption lists results for different dielectric constant ε_r values but does not state which values were used; specifying the ε_r values and the corresponding effective fields would make the sensitivity test reproducible.","section":"Extended Data Fig. 10 caption"},{"comment":"The spacing in 'V olkov' appears throughout the text and likely reflects a typesetting issue; the standard spelling 'Volkov' should be used consistently.","section":"Main text and Methods"},{"comment":"The caption contains a typographical artifact: 'around 65 ◦)' should be 'around 65°' or similar; this should be corrected during production.","section":"Fig. 2 caption"}],"recommendation":"major_revision","confidential_remarks":"The manuscript relies heavily on the authors' own prior theory methods (refs. 44, 60, 79, 80) and on closely related recent trARPES Floquet papers on graphene (refs. 49, 50). The distinction from those graphene studies is the valley and orbital-texture dependence, which is genuinely new. However, the quantitative headline claim should be made internally robust before publication; the current supporting material shows the sensitivity issue but does not resolve it."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"First, the good news: this is the first experiment I've seen that puts valley pseudospin into Floquet-Volkov interference, and it does it with a measurement protocol that is clever and mostly convincing. The polarization-resolved momentum microscopy data in Figs. 2 and 3 show a clear valley- and helicity-dependent sideband asymmetry, and the td-NEGF simulations reproduce the main features without fitting the valley asymmetry. The XUV CD-ARPES from dressed states is genuinely new, and the orbital-resolved analysis showing d_z2 weight in the sideband is a nice step. Data on Zenodo is a real plus.\n\nThe soft spot is exactly what the stress-test note says. The measured asymmetry at circular polarization is ~15%, but the headline claim in the main text is >50% Floquet valley polarization. That number comes from decomposing the calculated sideband into Floquet-only and Volkov contributions, and the Volkov background at circular polarization is large and set by the effective in-sample pump field from a Fresnel model. Extended Data Fig. 10 shows the valley-resolved Volkov signal changes with epsilon_r, but the paper never gives a range for epsilon_r across which the >50% claim survives. There are also no error bars on the measured asymmetry. And the body admits Volkov-only simulations reproduce most observed features, which makes 'unambiguously' in the abstract and conclusions stronger than the evidence supports.\n\nNone of this kills the qualitative result. The valley- and polarization-dependent interference near s-polarization, where Floquet and Volkov amplitudes are comparable, is exactly the regime where Floquet-Volkov interference should show up, and the opposite behavior at K and K' is a clear qualitative valley effect. The quantitative claim needs to be fenced in, not retracted.\n\nWho should read this: anyone working on Floquet engineering or valleytronics in TMDCs, and definitely the ultrafast photoemission crowd. The paper is a solid experimental contribution that will move the field. I'd send it to a serious referee; the conditions are manageable: put error bars on the asymmetry, run the decomposition over a range of epsilon_r, and calibrate the language.","headline":"First credible demonstration of valley-selective Floquet dressing in a TMDC, but the headline >50% polarization is an inferred decomposition, not a direct measurement—worth refereeing seriously.","tokens_in":22327,"tokens_out":2268,"would_cite":true,"duration_ms":18954,"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":"Circularly polarized, below-bandgap infrared pulses transiently create valley-polarized Floquet-Bloch states in the transition metal dichalcogenide 2H-WSe2, with the K and K′ valleys populated asymmetrically by more than 50% under the…","keywords":["Floquet-Bloch states","valleytronics","transition metal dichalcogenides","2H-WSe2","time- and angle-resolved photoemission","Volkov states","circular dichroism","time-dependent non-equilibrium Green's function"],"falsifier":"Using the same experimental data, determine the in-sample pump field from the known momentum dependence of the Volkov sideband (as in the paper's Extended Data Fig. 10) rather than from the assumed dielectric constant, and recompute the Floquet-only valley asymmetry; if the resulting valley polarization no longer exceeds 50%, the quantitative central claim would be falsified.","tokens_in":21200,"feed_emoji":"⚛️","tokens_out":10405,"duration_ms":81874,"temperature":0.7,"pith_summary":"Floquet engineering promises to create phases of matter that cannot be reached by equilibrium tuning, but valley-selective Floquet states—where the two K and K′ valleys of a transition metal dichalcogenide are dressed differently by circularly polarized light—had not been directly observed. This paper reports time- and polarization-resolved extreme ultraviolet momentum microscopy on 2H-WSe2 showing that below-bandgap 1.2 eV circularly polarized pump pulses create a first-order sideband whose intensity at the K and K′ valleys depends on the pump helicity. From that asymmetry, together with time-dependent non-equilibrium Green's function simulations, the authors infer valley-polarized Floquet-Bloch populations exceeding 50% under their conditions, and show that the sideband's orbital character acquires a conduction-band component—evidence of coherent dressing plus selection-rule-driven dynamics. The result would open a route to all-optical, transient control of valley pseudospin and of the associated Berry-curvature responses in layered semiconductors.","feed_headline":"Circular light creates >50% valley-polarized Floquet states","feed_subtitle":"Below-gap IR pulses make K and K' respond to opposite helicities, moving toward all-optical valley control.","key_machinery":"The load-bearing object is the first-order Floquet-Bloch sideband created by a sub-gap circularly polarized pump, detected through its quantum path interference with Volkov states—free-electron dressing of the outgoing photoelectron by the same pump pulse. That interference leaves a polarization-dependent modulation of the photoelectron angular distribution, which is the unambiguous marker of Floquet band formation. The theoretical engine is a time-dependent non-equilibrium Green's function (td-NEGF) simulation that treats both the pump dressing and the probe photoemission from first principles, including the momentum-dependent interband dipole matrix element (Berry connection) that carries the valley selection rules. An auxiliary Fresnel model for the pump field inside the sample sets the relative weight of Floquet and Volkov amplitudes; the valley asymmetry of the Floquet-only contribution is extracted from this decomposition.","core_discovery":"The central claim is that circularly polarized, below-bandgap infrared pulses transiently dress the electronic bands of 2H-WSe2 into valley-polarized Floquet-Bloch states. The paper demonstrates this through polarization-resolved photoemission: the first-order sideband (+ħω at 1.2 eV) shows a valley asymmetry that flips sign when the pump helicity goes from right- to left-circular, reaching about ±15% in sideband intensity. By decomposing the signal into Volkov (laser-assisted photoemission) and Floquet contributions in the td-NEGF simulations, the authors show that the Volkov part is helicity-independent, so the helicity-dependent asymmetry must come from the Floquet part, whose valley polarization they quantify as greater than 50%. They further report that XUV circular dichroism from these dressed states differs from the ground-state dichroism and reveals a momentum-dependent admixture of the conduction band's dz2 orbital into the sideband, a hybridization that standard Floquet spectral functions fail to reproduce and that the authors attribute to real-time population dynamics governed by valley-selective interband matrix elements.","pith_inferences":["A natural next test would be to use the Volkov angular distribution measured in the same dataset to calibrate the actual in-sample pump field, replacing the Fresnel assumption; the reported >50% valley polarization would then become a quantity tied to independently measured optical constants.","Because the hybridization tracks the momentum-dependent Berry connection, scanning the pump photon energy (as in the paper's detuning study) could turn this experiment into a map of how quantum geometry is modified by dressing, not just of band populations.","The same circularly-driven Floquet mechanism should leave a measurable imprint in transient optical probes, such as a helicity-dependent shift of excitonic resonances, so combining photoemission and transient absorption on the same sample would test whether the Floquet-only asymmetry extracted here is consistent with the optical Stark and Bloch-Siegert responses."],"forward_implications":["Circularly polarized, below-gap pulses become a direct all-optical knob for valley population in TMDCs, working without resonant excitation and on ultrafast timescales.","The transiently valley-polarized Floquet bands imply a nonequilibrium anomalous Hall response whose sign follows the pump helicity, so the same geometry could probe Berry-curvature transport out of equilibrium.","XUV circular dichroism of dressed states can serve as a general probe of orbital-texture changes in Floquet-engineered materials, not just in WSe2.","Polarization-resolved Floquet-Volkov interference provides a method to detect Floquet bands even when the dressing-induced gaps and band shifts are too small to resolve directly."],"supporting_citations":[{"why":"Prior observation of the valley-selective optical Stark effect in monolayer WS2; the paper extends this dressing concept to direct photoemission detection of Floquet-Bloch sidebands.","marker":"[27]"},{"why":"Established Floquet-Volkov quantum path interference as an unambiguous photoemission signature of Floquet bands; the method used here to identify the sidebands.","marker":"[28]"},{"why":"Provides the Volkov-sideband model (Bessel-function intensity) used to compute the helicity-independent Volkov contribution and its polarization dependence.","marker":"[48]"},{"why":"Observation of Floquet states in graphene and the Fresnel-based treatment of the in-sample pump field that the Floquet/Volkov decomposition relies on.","marker":"[50]"},{"why":"Explains the croissant-shaped photoelectron angular distributions and the orbital-pseudospin texture at K/K′ that the valley-resolved asymmetry is extracted from.","marker":"[60]"},{"why":"Supports modeling the near-surface Volkov dressing as the superposition of incoming and reflected pump fields in the Fresnel description.","marker":"[78]"},{"why":"Supplies the td-NEGF formula for the time-resolved photoemission signal used to simulate the measured Floquet-Volkov sidebands.","marker":"[79]"},{"why":"Provides the photoemission matrix elements used in the trARPES simulations, connecting the orbital content of the bands to the measured intensities.","marker":"[80]"}],"fun_headline_variants":["Circular IR pulses flip valley selectivity in WSe2","Floquet dressing yields >50% valley polarization","All-optical valley control via Floquet-Bloch states","Circular light dresses WSe2 into valley-polarized states"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The extraction of a >50% Floquet valley polarization hinges on the Fresnel model's assumed dielectric constant, which sets how strong the pump field is inside the sample and therefore how much of the measured sideband is assigned to Volkov processes; if the real in-sample field differs from that model, the Floquet-only asymmetry could move below 50%.","fun_headline_variants_meta":{"raw":{"variants":["Circular IR pulses flip valley selectivity in WSe2","Floquet dressing yields >50% valley polarization","All-optical valley control via Floquet-Bloch states","Circular light dresses WSe2 into valley-polarized states"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000672,"raw_usage":{"total_tokens":3116,"prompt_tokens":1057,"completion_tokens":2059,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":673,"completion_tokens_details":{"reasoning_tokens":1990}},"tokens_in":673,"tokens_out":2059,"duration_ms":14198,"temperature":1.0,"reasoning_tokens":1990,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-11T21:55:53.338474+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Using the same experimental data, determine the in-sample pump field from the known momentum dependence of the Volkov sideband (as in the paper's Extended Data Fig. 10) rather than from the assumed dielectric constant, and recompute the Floquet-only valley asymmetry; if the resulting valley polarization no longer exceeds 50%, the quantitative central claim would be falsified.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Established Floquet-Volkov quantum path interference as an unambiguous photoemission signature of Floquet bands; the method used here to identify the sidebands."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the Volkov-sideband model (Bessel-function intensity) used to compute the helicity-independent Volkov contribution and its polarization dependence."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Observation of Floquet states in graphene and the Fresnel-based treatment of the in-sample pump field that the Floquet/Volkov decomposition relies on."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supports modeling the near-surface Volkov dressing as the superposition of incoming and reflected pump fields in the Fresnel description."},{"cited_title":"& Sentef, M","cited_arxiv_id":null,"evidence_quote":"Supplies the td-NEGF formula for the time-resolved photoemission signal used to simulate the measured Floquet-Volkov sidebands."}],"review_version":1}