{"id":"7f35f3d2-fa81-4a7d-8c42-bc174d4291bd","arxiv_id":"2506.04697","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":7.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"400 nm light melts charge order in overdoped Bi2201 cuprates via orbital-selective photodoping, while 800 nm light does not, revealing a universal electronic instability.","lead":"This paper shows that in an overdoped copper-oxide superconductor, only certain light colors can melt its charge order: 400 nm pulses do, 800 nm pulses do not. The difference points to which electronic orbitals the light excites, and suggests the same underlying electronic instability seen in underdoped materials.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The ~3 ps 'CO recovery' in overdoped Bi2201 is extracted from Eq. (2) with the 2 ps lattice-thermal timescale fixed from literature; if the slow exponential trades against that thermal term, the universal-instability claim loses its foundation.","rationale":"Read in good faith, the core observation is well supported: 400 nm and 800 nm pumps give different Q_CO responses at comparable absorbed-photon densities, the scattering/fluorescence normalization addresses the dominant XAS artifact, and the off-momentum control is appropriate. The orbital-selective photodoping mechanism is plausible but not directly probed; however, the universal-instability claim depends mainly on the extracted ~3 ps CO recovery time. That number comes from Eq. (2), a multi-component fit in which the slow recovery and the thermal term are both obtained from the same scattering trace, with the thermal timescale fixed from literature. This is exactly the assumption the reader flagged, and I agree with that identification: a 3 ps exponential and a 2 ps thermal rise in an 8 ps window are not cleanly separable without an independent constraint. The concern is load-bearing but addressable by a re-analysis of the existing data, so it supports a CONDITIONAL reading rather than rejection. The reader's verdict already reflects this conditionality, so no verdict change is needed.","tokens_in":15600,"tokens_out":6830,"duration_ms":90310,"concrete_test":"Refit the 400 nm Q_CO data of Fig. 3c with Eq. (2) under two perturbations: (i) leave tau' free instead of fixing it at 2 ps; (ii) fix A1 and tau_r1 to the parameters obtained from the simultaneously recorded fluorescence trace, then refit the residual as A2 exp(-t/tau_r2) - A'(1 - exp(-t/tau')) with tau' free. Compare AIC/BIC and the profile likelihood for tau_r2, and require that the 95% confidence interval for tau_r2 remains near 3 ps and excludes timescales below 1 ps across tau' in 0.5-10 ps. If tau_r2 instead trades against tau' or A', the 3 ps CO-recovery assignment is underdetermined.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's central claim that the ~3 ps slow recovery at Q_CO represents CO reconstruction, and hence that overdoped and underdoped cuprates share a universal electronic instability, rests on the decomposition in Eq. (2). In that fit, the slow 'CO' term A2 exp(-t/tau_r2) and the rising thermal term A'(1 - exp(-t/tau')) are both extracted from the same scattering trace, with tau' fixed at ~2 ps from Refs. [39,40] rather than measured on this sample. Over the displayed 0-8 ps window, a 3 ps exponential decay and a 2 ps rising thermal term are strongly overlapping functions: the two time constants differ by less than a factor of two, so A2, A' and tau_r2 are not independently constrained by the plotted data. The orange thermal curve in Fig. 3c is a model output, not an independent lattice-temperature measurement. Supplementary Fig. 7 also shows a small ~1% offset that persists to 500 ps; depending on how that offset is assigned, it can absorb slowly varying signal and shift the fitted tau_r2. The paper itself acknowledges in the Discussion that disentangling electronic and lattice contributions requires future phonon-resonant experiments, which is precisely the step that is unsecured here. If tau_r2 is not identifiable once tau' is allowed to vary or once the electronic component is fixed from the simultaneous fluorescence trace, the comparison to underdoped YBCO in Fig. 3d and the universality conclusion lose direct support. This is a load-bearing concern, though not a refutation: the wavelength-dependent melting itself is credible; the vulnerable step is the assignment of the recovery timescale.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports time-resolved resonant X-ray scattering (tr-REXS) and time-resolved X-ray absorption spectroscopy (tr-XAS) on overdoped (Bi,Pb)2.12Sr1.88CuO6+δ (Tc≈11 K). The authors find that 800 nm excitation produces only a uniform, XAS-related suppression of the scattering and fluorescence signals, with no change in the charge-order (CO) peak after normalization, whereas 400 nm excitation melts the CO peak in a fluence-dependent manner. The CO recovery time is reported as ~3 ps, similar to underdoped cuprates, and the authors interpret this as evidence for a universal electronic instability across the cuprate phase diagram. They further propose that 400 nm light drives orbital-selective photodoping from the Zhang-Rice singlet band to the upper Hubbard band or apical oxygen states, transiently changing the in-plane doping, while 800 nm light lacks the energy to do so. The higher fluence required to melt overdoped CO is attributed to increased lattice coupling.","tokens_in":15979,"tokens_out":7591,"duration_ms":82876,"significance":"The central observation—the strong dependence of CO melting on pump photon energy—is well supported by the raw scattering and fluorescence data, the normalization procedure, and the momentum dependence at Q=0.08 r.l.u. If the 3 ps recovery time holds, the comparison to underdoped cuprates is an important step toward unifying the physics of charge order across the phase diagram. The paper also includes careful estimates of absorbed photon density per Cu site and a control away from Q_CO, which strengthen the assignment. However, the 3 ps value is extracted from a multi-exponential fit with a fixed thermal timescale, and the orbital-selective mechanism is inferred from static and transient XAS without direct spectral-weight quantification; both points need to be addressed before the universality claim is fully convincing.","major_comments":[{"comment":"The decomposition in Eq. (2) that separates the slow recovery (tau_r2 ~ 3 ps) from the thermal term with tau' fixed at ~2 ps is not identifiable from the data shown. Over the displayed 0-8 ps window, the two exponentials have comparable time constants, and the orange thermal curve in Fig. 3c is a model output rather than an independent lattice-temperature measurement. Because tau' is taken from refs [39,40] rather than measured on this sample, A2, A', and tau_r2 can trade off; the ~1% offset persisting to 500 ps in Supplementary Fig. 7 could further absorb slowly varying signal. The authors should show that tau_r2 is stable when (i) tau' is left free, (ii) a baseline offset is included, or (iii) A' is constrained by a separate non-resonant probe. As written, the comparison to underdoped YBCO in Fig. 3d and the claim of a universal electronic instability rest on an unsecured decomposition.","section":"CO dynamics dependence on pump laser wavelength and fluence (Eq. 2, Fig. 3c)"},{"comment":"The orbital-selective photodoping mechanism is inferred rather than directly evidenced. The transient O K-edge XAS in Fig. 4b shows changes in the ZRS peak, but the difference spectra are not quantified, and no resolved changes in the UHB or apical-oxygen states are presented. The conclusion that 400 nm depletes the ZRS band while 800 nm fills it is based on the relative amplitude of the ZRS suppression, and the assignment of the 400 nm transition to ZRS-to-UHB or ZRS-to-apical transfer relies on energetics and theory (ref 46). The authors should either provide quantitative spectral-weight analysis or explicitly label this mechanism as a hypothesis. This is central to the title's claim of 'orbital-selective photodoping.'","section":"DISCUSSION (Fig. 4b)"},{"comment":"The CO recovery time is extracted from the intensity at a single momentum Q_CO, but the peak width and position are only reported at Δt=0.25 ps (Fig. 2c). If the CO peak broadens or shifts at later delays, the fixed-momentum intensity trace would not represent the CO order parameter alone. The authors should either measure time-resolved H scans at selected delays to confirm the lineshape remains constant throughout the recovery, or justify why a transient lineshape change cannot mimic the slow recovery component.","section":"CO dynamics dependence on pump laser wavelength and fluence (Fig. 2c, Fig. 3)"}],"minor_comments":[{"comment":"The word 'sourse' in the Methods section should be 'source'.","section":"Methods (sample characterization)"},{"comment":"The phrase 'scattering signals bare fitted with the Lorentzian function' should read 'scattering signals are fitted with the Lorentzian function'.","section":"Fig. 1c caption"},{"comment":"The sentence 'The photoinduced shift of the UHB peak (~80.3±10.1 meV) are similar' should use the singular 'is similar'.","section":"Supplementary Note 1"}],"recommendation":"major_revision","confidential_remarks":"This paper presents a striking wavelength-dependent CO melting result with careful normalization and appropriate momentum controls. The main concerns are the identifiability of the 3 ps recovery component from Eq. (2) and the indirectness of the orbital-selective mechanism. If the authors can address the fitting degeneracy with additional analysis or data, the paper would be suitable for a high-impact venue. The current version overstates the universality claim given the unresolved decomposition."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague, this one is worth a serious look. The central observation—that 400 nm pump melts charge order in overdoped Bi2201 while 800 nm does not, even at higher absorbed photon density—is well supported and genuinely new. The normalization of scattering by fluorescence, the momentum check away from Q_CO, and the fluence series are the right controls. The XAS redshift and sub-ps recovery are consistent with prior work. That part is solid.  What's less secure is the assignment of the ~3 ps slow recovery to CO reconstruction. Eq. (2) has two exponentials and a rising thermal term, with tau' fixed at ~2 ps from literature on other compounds. The plotted window is 0-8 ps, so a 3 ps decay and 2 ps rise are strongly overlapping. A2, A', and tau_r2 are not independently identified from this trace alone. The momentum dependence at Q=0.08 helps—the slow component disappears there—but the fit decomposition still carries the load. The 1% offset that persists to 500 ps (Supp. Fig. 7) could also absorb slow signal, though the authors mention it and assign it to out-of-plane transfer. So the universal-instability claim, which rests on the 3 ps value matching underdoped YBCO, is plausible but not established. The comparison itself is apples-to-oranges: different compound, different pump wavelength, different fluence.  The orbital-selective photodoping mechanism is inferred, not directly probed. The O K-edge XAS and optical conductivity support the energy-level picture, and the citation to the orbitally selective photodoping paper is appropriate. But the mechanism remains an interpretation. That's fine for a letter; it's clearly labeled as such.  The paper's own Discussion concedes that disentangling electronic and lattice contributions needs phonon-resonant experiments. I read that as honest, not as fatal.  So: who's this for? Cuprate dynamics people and anyone working on light control of charge order. It deserves peer review. A good referee should push on Eq. (2), ask for fits with tau' free or with the electronic component fixed from the fluorescence channel, and check the sensitivity of tau_r2 to the long-time offset. If those hold, the wavelength dependence alone is a publishable result.  I'd take it. Verdict: conditionally accept after the fit identifiability is addressed.","headline":"Wavelength-dependent photodoping result is credible and new, but the ~3 ps 'CO recovery' is the least secure link and the universality claim outruns the data.","tokens_in":16547,"tokens_out":1467,"would_cite":true,"duration_ms":17910,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["74.72.-h","78.47.J-"],"model":"deepseek-v4-flash","headline":"In overdoped cuprates, 400 nm light melts the charge order while 800 nm light cannot, revealing an orbital-selective photodoping mechanism and a ~3 ps recovery time that matches underdoped cuprates.","keywords":["charge order","cuprate superconductors","ultrafast dynamics","resonant X-ray scattering","time-resolved X-ray absorption","orbital-selective photodoping","charge-transfer gap","overdoped Bi2201"],"falsifier":"Measure the lattice temperature independently after 400 nm excitation—for example, via time-resolved X-ray thermal diffuse scattering or a phonon-sensitive probe—and check whether the thermal recovery actually has a ~2 ps timescale. If the thermal timescale is materially different, the two-exponential decomposition in Eq. (2) is not identifiable, and the 3 ps component cannot be assigned to charge-order reconstruction. A complementary check: scan the pump photon energy from 1.55 eV to 3.1 eV and verify that CO melting onsets at the ~2 eV charge-transfer gap; if melting appears below the gap, the orbital-selectivity interpretation fails.","tokens_in":15378,"feed_emoji":"⚡","tokens_out":7117,"duration_ms":75232,"temperature":0.7,"pith_summary":"This paper reports that in the overdoped cuprate (Bi,Pb)$_{2.12}$Sr$_{1.88}$CuO$_{6+\\delta}$, only 400 nm (3.1 eV) light can melt the charge order, while 800 nm (1.55 eV) light cannot, even at higher absorbed photon densities. The authors argue that 400 nm photons carry enough energy to drive electrons from the Zhang-Rice singlet band into the upper Hubbard band or onto apical oxygen orbitals, transiently changing the doping level and suppressing the charge-order amplitude without altering its period or correlation length. The charge order recovers in about 3 ps, the same timescale seen in underdoped cuprates, which the authors take as evidence for a common electronic instability across the doping phase diagram. They also find that melting the overdoped charge order requires an order of magnitude higher fluence than in underdoped samples, pointing to a stronger role of lattice interactions at high doping.","feed_headline":"400 nm light melts charge order where 800 nm light fails","feed_subtitle":"Ultrafast orbital-selective photodoping reveals a ~3 ps recovery shared with underdoped cuprates.","key_machinery":"The argument is carried by combining time-resolved resonant X-ray scattering (tr-REXS) at the Cu $L_3$ edge with time-resolved X-ray absorption spectroscopy (tr-XAS), comparing the CO peak dynamics with the fluorescence (XAS) dynamics. The central mechanism is orbital-selective photodoping: 400 nm (3.1 eV) photons exceed the charge-transfer gap $\\Delta_{\\mathrm{CT}} \\approx 2$ eV and transfer electrons from the Zhang-Rice singlet band (a hybrid Cu-O orbital band) to the upper Hubbard band or apical oxygen $2p_z$ states, transiently increasing planar hole doping; 800 nm (1.55 eV) photons lack this energy and only populate the Zhang-Rice band. The CO-specific recovery is extracted by fitting the pump-probe trace with two exponentials plus a thermal term whose timescale ($\\sim$2 ps) is fixed from prior literature.","core_discovery":"The central finding is an excitation-energy-selective melting of charge order in overdoped Bi2201: 400 nm pump pulses suppress the resonant X-ray scattering peak at $Q_{\\mathrm{CO}}$, while 800 nm pulses leave it unchanged after accounting for the transient X-ray absorption shift. The selectivity is traced to orbital character: 400 nm light crosses the ~2 eV charge-transfer gap and promotes electrons out of the Zhang-Rice singlet band (or out of the CuO$_2$ planes into apical oxygen states), effectively photodoping the planes, whereas 800 nm light only excites electrons within the O $2p$ manifold into the Zhang-Rice band and does not remove holes from the planes. The ~3 ps recovery of the CO peak after 400 nm excitation matches underdoped YBa$_2$Cu$_3$O$_{6.67}$ and striped nickelates, supporting a universal electronic origin for charge order, while the roughly tenfold higher fluence needed in the overdoped sample indicates that lattice coupling contributes to CO stability at high hole doping.","pith_inferences":["If the 3 ps recovery really is doping-independent, the difference between underdoped and overdoped CO is not its electronic origin but the stiffness added by lattice coupling; a direct test would be to measure the CO recovery time after exciting a specific phonon mode.","The near-identical absorbed-photon densities for 800 nm and 400 nm (0.11 vs 0.14 photons/Cu at 5 mJ/cm$^2$) make a purely thermal or absorbed-energy explanation of the wavelength dependence implausible; this could be checked with a two-pulse experiment that first heats the lattice with 800 nm and then probes whether the CO melting threshold shifts.","The slow component that persists to 500 ps after 400 nm excitation suggests a long-lived out-of-plane charge transfer; if exploitable, this could be used to create metastable superconducting-like states, but the paper does not establish such an effect.","The robustness of overdoped CO to 0.1 mJ/cm$^2$, which easily melts underdoped CO, implies that any search for photo-enhanced superconductivity in overdoped cuprates should use pump energies above the charge-transfer gap, not the near-infrared wavelengths commonly used for underdoped samples."],"forward_implications":["If the ~3 ps recovery is genuine, charge order in overdoped and underdoped cuprates share the same electronic recovery timescale, indicating a common origin for the ordered state across the phase diagram.","Orbital-selective photodoping can transiently change the in-plane doping level without disturbing the CO period or correlation length, offering a nonthermal control knob for the ordered phase.","The order-of-magnitude higher fluence required to melt overdoped CO implies that lattice degrees of freedom stabilize CO at high doping, so phonon-resonant or mid-infrared pumping should be able to disentangle electronic and lattice contributions.","Tuning pump photon energy to specific interband transitions of different orbital character can be used to selectively manipulate intertwined orders (charge, spin, nematicity) in other correlated materials such as nickelates, kagome metals, and iron-based superconductors.","Light-induced CO melting in the overdoped regime may transiently enhance superconductivity, in analogy to underdoped cuprates."],"supporting_citations":[{"why":"Equilibrium resonant X-ray scattering study that established charge order in overdoped (Bi,Pb)2.12Sr1.88CuO6+δ; supplies the CO peak position, momentum, and the robustness against temperature that motivate this work.","marker":"[25]"},{"why":"Time-resolved XAS study of a cuprate showing photoinduced renormalization of on-site Coulomb repulsion; provides the method and the electronic recovery timescale (holon-doublon recombination) used to separate the XAS-shift contribution.","marker":"[27]"},{"why":"Theoretical prediction of orbitally selective resonant photodoping that transiently redistributes holes from CuO2 planes to charge reservoir layers; the mechanism the paper invokes to explain 400 nm melting.","marker":"[46]"},{"why":"Time-resolved REXS measurement of underdoped YBa2Cu3O6.67 showing ~3 ps CO recovery; the comparison target for the claimed universal electronic instability.","marker":"[15]"},{"why":"Time-resolved REXS study of La2−xBaxCuO4 demonstrating low-fluence diffusive CO dynamics in underdoped cuprates; supplies the baseline fluence and dynamic behavior against which overdoped CO is judged robust.","marker":"[33]"},{"why":"Theoretical work proposing that charge density waves in extremely overdoped cuprates are driven by phonons; supports the paper's attribution of overdoped CO stability to lattice interactions.","marker":"[55]"}],"fun_headline_variants":["400 nm melts charge order, 800 nm doesn't: orbital-selective","Pump color selects charge-order melting in overdoped cuprates","Orbital-selective photodoping melts charge order: 400 vs 800 nm","Ultrafast melt of charge order needs 400 nm, not 800 nm light","Overdoped cuprate charge order melts with 400 nm, not 800 nm"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The ~3 ps charge-order recovery time is extracted by assuming the pump-probe trace separates into a fast electronic recovery, a slow CO recovery, and a thermal background whose ~2 ps timescale is taken from earlier literature; if the thermal timescale is wrong or the two recovery processes overlap, the 3 ps value and the universality claim attached to it lose support.","fun_headline_variants_meta":{"raw":{"variants":["400 nm melts charge order, 800 nm doesn't: orbital-selective","Pump color selects charge-order melting in overdoped cuprates","Orbital-selective photodoping melts charge order: 400 vs 800 nm","Ultrafast melt of charge order needs 400 nm, not 800 nm light","Overdoped cuprate charge order melts with 400 nm, not 800 nm"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000771,"raw_usage":{"total_tokens":3444,"prompt_tokens":1003,"completion_tokens":2441,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":619,"completion_tokens_details":{"reasoning_tokens":2334}},"tokens_in":619,"tokens_out":2441,"duration_ms":18044,"temperature":1.0,"reasoning_tokens":2334,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-07T10:35:41.799687+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the lattice temperature independently after 400 nm excitation—for example, via time-resolved X-ray thermal diffuse scattering or a phonon-sensitive probe—and check whether the thermal recovery actually has a ~2 ps timescale. If the thermal timescale is materially different, the two-exponential decomposition in Eq. (2) is not identifiable, and the 3 ps component cannot be assigned to charge-order reconstruction. A complementary check: scan the pump photon energy from 1.55 eV to 3.1 eV and verify that CO melting onsets at the ~2 eV charge-transfer gap; if melting appears below the gap, the orbital-selectivity interpretation fails.","supporting_citations":[{"cited_title":"Mater.17, 697–702 (2018)","cited_arxiv_id":null,"evidence_quote":"Equilibrium resonant X-ray scattering study that established charge order in overdoped (Bi,Pb)2.12Sr1.88CuO6+δ; supplies the CO peak position, momentum, and the robustness against temperature that motivate this work."},{"cited_title":"R.et al.Ultrafast renormalization of the on-site coulomb repulsion in a cuprate superconductor","cited_arxiv_id":null,"evidence_quote":"Time-resolved XAS study of a cuprate showing photoinduced renormalization of on-site Coulomb repulsion; provides the method and the electronic recovery timescale (holon-doublon recombination) used to separate the XAS-shift contribution."},{"cited_title":"& Devereaux, T","cited_arxiv_id":null,"evidence_quote":"Theoretical prediction of orbitally selective resonant photodoping that transiently redistributes holes from CuO2 planes to charge reservoir layers; the mechanism the paper invokes to explain 400 nm melting."},{"cited_title":"L., Hinton, J","cited_arxiv_id":null,"evidence_quote":"Time-resolved REXS measurement of underdoped YBa2Cu3O6.67 showing ~3 ps CO recovery; the comparison target for the claimed universal electronic instability."},{"cited_title":"Adv.5, eaax3346 (2019)","cited_arxiv_id":null,"evidence_quote":"Time-resolved REXS study of La2−xBaxCuO4 demonstrating low-fluence diffusive CO dynamics in underdoped cuprates; supplies the baseline fluence and dynamic behavior against which overdoped CO is judged robust."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Theoretical work proposing that charge density waves in extremely overdoped cuprates are driven by phonons; supports the paper's attribution of overdoped CO stability to lattice interactions."}],"review_version":1}