{"id":"14496b93-cf96-49a9-9e3c-37a895e43b8e","arxiv_id":"2507.08756","paper_version":2,"verdict":"ACCEPT","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"low","formal_verification":"none","parameter_count":1,"one_line_summary":"Copper substitution linearly suppresses the density wave transition in La4Ni3O10 and releases mobile holes, but does not by itself induce superconductivity.","lead":"By replacing some nickel atoms with copper in the three-layer nickelate La4Ni3O10, the paper shows that the material's density wave transition is steadily suppressed and its mobile carrier count rises sharply. The result gives a new chemical knob for studying what else is needed to make this nickelate family superconducting.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Hall-derived 'carrier delocalization' rests on single-band analysis at one temperature; multiband and mobility effects are not excluded.","rationale":"The reader's weakest_assumption identified both the susceptibility-kink interpretation and the Hall-carrier interpretation as fragile. I agree with both, but the Hall issue is the more load-bearing because it supports the paper's central mechanistic claim that density-wave suppression releases carriers, stated in the abstract and Discussion. The susceptibility-kink persistence is also questionable—it may reflect a broadened resistive transition rather than true spin-charge decoupling—but the authors themselves hedge this point and call for neutron/cryo-TEM studies, so the claim is appropriately qualified. The Hall argument, by contrast, is presented as a quantitative conclusion: the factor-of-100 discrepancy with oxygen doping is used to argue that DW suppression plays a central role in carrier delocalization. That argument is not secure without a multiband transport analysis or temperature/field-dependent Hall data. A two-band fit would directly test whether the R_H change is a carrier-density effect or a mobility/Fermi-surface reconstruction effect. If the concern lands, the primary experimental observations (linear Tdw suppression, persistence of the susceptibility anomaly, absence of superconductivity) remain valuable, but the interpretation should be softened from 'carrier delocalization' to 'a Hall response change that may reflect Fermi-surface reconstruction, mobility changes, or genuine carrier release.' Therefore I recommend CONDITIONAL rather than REJECT: the data merit publication, but the mechanistic inference should be revised or explicitly labeled as one of several possibilities pending the proposed Hall analysis.","tokens_in":8208,"tokens_out":7022,"duration_ms":90387,"concrete_test":"Measure the Hall coefficient as a function of temperature (1.8–300 K) and magnetic field (±14 T) on x = 0, 0.15, and 0.30 samples, and fit the field dependence with a two-band model to extract separate densities and mobilities for electron and hole pockets. If the fitted net hole density n_h − n_e is unchanged with x while the single-field R_H tracks the reported 10^22 cm^-3 increase, the delocalization interpretation is refuted; if the net carrier density genuinely rises by that amount, the concern is settled in the paper's favor.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The paper's most distinctive quantitative claim is that Cu substitution releases ~10^22 cm^-3 mobile carriers, two orders of magnitude more than the ~10^20 cm^-3 expected from oxygen excess. This inference assumes that the Hall carrier concentration n = 1/(e R_H), measured only at 1.8 K, directly measures the density of mobile holes. La4Ni3O10 is a multiband metal in which the density wave reconstructs the Fermi surface; R_H is set by the balance of electron and hole pockets and their mobilities, not simply by carrier count. Cu substitution broadens the resistive transition (Fig. 1) and introduces disorder, so mobility changes alone could account for a large R_H shift without any genuine delocalization. The oxygen-stoichiometry comparison also ignores that Cu substitution itself can alter carrier count if Cu is not strictly isovalent with Ni, and that δ from TGA carries substantial uncertainty. The plateau in n at x≈0.3, used to link carrier enhancement to density-wave suppression, could instead reflect a mobility crossover or a solubility limit. Because the central mechanistic conclusion—suppression of the density wave delocalizes bound carriers—depends on this Hall interpretation, the concern is load-bearing.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports a systematic Cu-substitution study of polycrystalline La4Ni3-xCuxO10+δ (0 ≤ x ≤ 0.7) using resistivity, magnetic susceptibility, Hall effect, TGA, and TEM. The density-wave transition temperature Tdw decreases approximately linearly with Cu content at a rate of about -13.8 K per 1% Cu (R² = 0.98), and the resistive anomaly is nearly suppressed by x ≈ 0.15-0.20, while a magnetic susceptibility anomaly persists until x ≈ 0.3. The Hall carrier concentration at 1.8 K increases with x and plateaus near x ≈ 0.3, coinciding with the full suppression of the magnetic anomaly. No superconductivity is observed across the series. The authors interpret these observations as evidence for partial spin-charge decoupling of the density wave and for carrier delocalization caused by density-wave suppression.","tokens_in":8356,"tokens_out":5000,"duration_ms":62370,"significance":"If substantiated, the paper provides a useful ambient-pressure chemical tuning route for the intertwined density waves in trilayer nickelates, and its phase diagram offers empirical constraints on the competition between density-wave order and superconductivity in pressurized La4Ni3O10. The systematic series, the cross-correlated transport and magnetization determinations of Tdw, the quantitative linear suppression slope, and the explicit reporting of secondary-phase formation at high x are valuable strengths. The central observations are direct measurements, and no model fitting or derived parameters are used to define the main phase-diagram result.","major_comments":[{"comment":"The quantitative claim that Cu substitution releases roughly 10^22 cm^-3 mobile carriers, two orders of magnitude beyond what oxygen nonstoichiometry can supply, rests on the single-band Hall expression n = 1/(eR_H) evaluated only at 1.8 K. In a multiband metal with a reconstructed Fermi surface, R_H is set by the balance of electron and hole pockets and their mobilities, not simply by carrier density, and Cu-induced disorder (which visibly broadens the resistive transition in Fig. 1) can change mobilities independently. The paper reports neither R_H(T) nor R_H(B), and no two-band or mobility analysis is performed, so the specific mechanism of carrier delocalization is not uniquely supported by the data. I recommend providing field- and temperature-dependent Hall measurements, assessing multiband/mobility effects, and propagating uncertainties in δ before drawing the delocalization conclusion.","section":"Results, Fig. 2c and Discussion (\"One potential explanation\")"},{"comment":"The partial spin-charge decoupling conclusion rests on the absence of a resistive anomaly at x > 0.15 and the persistence of a \"subtle kink\" in χ(T). Because the resistive anomaly broadens with Cu content (Fig. 1), its apparent disappearance could be a detection-threshold or background-subtraction effect rather than a genuine decoupling. In addition, the χ anomaly is weak, and no statistical significance, peak-fitting criterion, or alternative background model is presented for the derivative features. Without a direct probe of charge order (e.g., diffraction or local structural measurements), the assignment of the resistive anomaly to the charge component and the susceptibility anomaly to the spin component remains an assumption. The authors should either temper the abstract-level claim of spin-charge decoupling or provide a more quantitative analysis of the anomaly detection limits.","section":"Results, Fig. 3 and Discussion (\"A notable divergence\")"}],"minor_comments":[{"comment":"The threshold for the disappearance of the resistive anomaly is stated as x > 0.15 in the abstract and Results, but the Fig. 4 caption says the resistive transition \"vanishes near x ≈ 0.20.\" Please standardize this value.","section":"Abstract and Fig. 4 caption"},{"comment":"The formula \"La4Ni3-xCuxO10-δ\" is inconsistent with the \"+δ\" notation used elsewhere in the paper; this should be corrected.","section":"Methods, first paragraph"},{"comment":"TGA is described as shown only for x = 0 (Fig. S2), yet Fig. 2d plots δ as a function of x for the full series. Please clarify how the oxygen non-stoichiometry was determined for the Cu-substituted samples and include error bars.","section":"Results, Fig. 2d"},{"comment":"The linear fit to the Hall carrier concentration for 0 ≤ x ≤ 0.36 is mentioned but the fit parameters and error bars are not given; please include them in the figure or caption.","section":"Results, Fig. 2c"},{"comment":"Reference 33 lists a composition La4Ni2.25Cu0.75O10+δ while the text primarily discusses x = 0.7; please align the notation consistently.","section":"References and Supplemental Material"}],"recommendation":"major_revision","confidential_remarks":"The paper reports a clean, systematic experimental series and the phase diagram is likely to be reproducible. The main uncertainty is whether the Hall-based carrier-delocalization claim and the spin-charge decoupling interpretation are strong enough for the prominence they receive in the abstract and discussion. In revision, the authors should either supply additional Hall data (T- and field-dependent, with multiband considerations) and a more quantitative treatment of the susceptibility anomaly, or explicitly reframe these as suggestive rather than established conclusions."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The genuinely new thing here is the Cu substitution series: nobody had mapped T_dw, carrier density, and oxygen stoichiometry across x in La4Ni3-xCuxO10 before, and the linear suppression at ~-13.8 K per 1% Cu (R²=0.98) is a clean, internally consistent result. The transport, magnetization, and Hall data all move together in the low-x regime, and the authors are appropriately cautious in the discussion about what drives the suppression (doping vs. disorder). The null result—no superconductivity up to x=0.7—is reported conservatively and used to make a sensible structural-transition point. I think the reader's ACCEPT verdict is right. Where I would push back gently is the Hall interpretation. The paper argues that the ~10^22 cm^-3 increase in carrier concentration is far larger than the ~10^20 cm^-3 expected from excess oxygen, so density-wave suppression must delocalize carriers. That claim assumes n = 1/(eR_H) at 1.8 K is a clean carrier count in a multiband, reconstructed metal. Cu disorder broadens the resistive transition and almost certainly changes mobilities and pocket balances, so part of the R_H shift could be a mobility or multiband effect rather than a genuine release of localized carriers. The plateau at x≈0.3 could also be a solubility or mobility crossover. The authors do hedge, and they call for neutron and cryo-TEM work, so the paper is not overclaiming in a deceptive way. But the delocalization language is a bit strong for what is still a single-temperature, single-field Hall measurement on polycrystals. I would want to see a two-band analysis or optical conductivity or a temperature-dependent Hall series before taking that specific mechanism to the bank. The softer spots: the spin-charge decoupling at x>0.15 rests on a subtle susceptibility kink surviving when the resistive anomaly vanishes. That could be a spurious impurity tail or simply a broader transition in polycrystalline samples; the authors themselves note the susceptibility transition does not broaden with Cu, which is a little odd and worth probing. The TGA-derived δ values carry real uncertainty, and the comparison to oxygen-only doping is a rough estimate. Citation pattern looks fine—they engage the relevant pressure, film, and cuprate literature and do not hide the Al-doping work. Methods are described well enough to reproduce the synthesis and measurements, though raw data are not deposited. Bottom line: this is a solid experimental contribution for the nickelate community, and the main phase diagram result is likely to stand regardless of how the Hall interpretation shakes out. I would send it to peer review; a good referee should push on the Hall analysis and ask for more evidence on the decoupling claim, but the paper deserves a place in the literature even if the carrier-delocalization narrative is softened.","headline":"A careful, useful Cu-substitution phase diagram for La4Ni3O10 with a plausible but not fully proven spin-charge decoupling claim; the Hall-based carrier-delocalization argument deserves scrutiny but does not sink the paper.","tokens_in":844,"tokens_out":916,"would_cite":true,"duration_ms":22716,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["75.30.Fv","71.27.+a","72.15.Gd"],"model":"deepseek-v4-flash","headline":"Copper substitution suppresses intertwined density waves in a trilayer nickelate and partially decouples their spin and charge parts.","keywords":["nickelate superconductivity","density wave","spin-charge decoupling","chemical substitution","Hall effect","trilayer Ruddlesden-Popper","carrier delocalization","La4Ni3O10"],"falsifier":"A neutron or muon measurement on La4Ni2.7Cu0.3O10+δ that finds no incommensurate magnetic order and no diffuse spin correlations would falsify the claim of surviving short-range spin correlations; alternatively, detecting a copper-oxide or nickel-oxide impurity phase that accounts for the susceptibility kink, or showing that the Hall carrier density changes strongly with oxygen annealing, would undermine the carrier-delocalization argument.","tokens_in":7981,"feed_emoji":"🧲","tokens_out":7325,"duration_ms":74722,"temperature":0.7,"pith_summary":"This paper reports that substituting copper for nickel in the trilayer nickelate La4Ni3O10 suppresses its intertwined spin- and charge-density-wave order in a controlled, linear way. The density-wave transition temperature falls by about 13.8 K for every 1% of copper, and the resistive anomaly disappears above x≈0.15 while a magnetic susceptibility signature lingers until x≈0.3. The measured Hall carrier concentration rises by roughly two orders of magnitude more than oxygen nonstoichiometry can account for, implying that melting the density wave releases previously localized holes. No superconductivity appears for copper contents up to x=0.7, suggesting that suppressing the density waves alone is not enough to stabilize the superconducting state.","feed_headline":"Copper doping kills density waves in nickelate at 14 K per percent","feed_subtitle":"The density-wave transition disappears while magnetic order lingers, and no superconductivity follows.","key_machinery":"The central object is the trilayer Ruddlesden-Popper nickelate La4Ni3-xCuxO10+δ, whose intertwined spin-density wave (SDW) and charge-density wave (CDW) can be tracked by kinks in resistivity and magnetic susceptibility. The paper uses the minimum in dρ/dT to define Tdw and the corresponding kink in χ(T) to follow the magnetic component, while Hall effect at 1.8 K gives the carrier density and thermogravimetric analysis gives oxygen stoichiometry. The key comparison is the linear suppression of Tdw versus x, its match with the pressure-suppression rate, and the divergence between transport and magnetic signatures at intermediate x, which is the evidence for spin-charge decoupling.","core_discovery":"In La4Ni3-xCuxO10+δ, copper substitution acts as a chemical tuning knob for the intertwined density wave order of the parent compound. The authors find a linear suppression rate of Tdw ≈ -13.8 K per 1% Cu (R²=0.98), with resistive and magnetic signatures staying in agreement at low x. Above x≈0.15 the resistivity anomaly is no longer detectable, yet the magnetic susceptibility kink persists until x≈0.3, which the authors interpret as a partial decoupling of charge and spin components with short-range spin correlations surviving. Hall measurements at 1.8 K show a carrier concentration that rises linearly with x and then plateaus exactly where the magnetic anomaly vanishes, and thermogravimetric analysis shows that oxygen uptake contributes too little to explain the carrier increase. The absence of superconductivity across the whole series is contrasted with pressure experiments, pointing to the structural transition from monoclinic P21/a to tetragonal I4/mmm as an additional requirement.","pith_inferences":["If the surviving susceptibility kink indeed reflects short-range spin correlations, neutron and muon experiments on x≈0.2–0.3 samples should find broad, inelastic magnetic scattering rather than a sharp magnetic Bragg peak.","The coincidence between the carrier-density plateau and the disappearance of the magnetic anomaly suggests that the Hall concentration at 1.8 K could serve as a bulk thermodynamic-like probe of density-wave melting in related nickelates.","The linear suppression rate of about -13.8 K per 1% Cu is close to the pressure rate of about -13 K/GPa; if the mechanism is lattice compression, applying pressure to a lightly Cu-substituted sample might mimic higher pressure and possibly reach superconductivity at lower pressures.","A testable extension would be to measure the optical conductivity or Seebeck coefficient across x to independently confirm the delocalization of carriers and identify whether the released holes form a coherent metallic state."],"forward_implications":["The density-wave order in La4Ni3O10 can be tuned continuously by chemical substitution, providing a route to study the phase diagram without high pressure.","At x between 0.15 and 0.3, a regime exists with no detectable charge-order resistive anomaly but a persistent magnetic signature, indicating a window of partially decoupled spin and charge degrees of freedom.","The jump in mobile carrier concentration upon density-wave suppression can be much larger than nominal doping, so transport experiments should account for delocalized carriers.","Because no superconductivity appears despite full density-wave suppression, the monoclinic-to-tetragonal structural transition likely plays an essential role in stabilizing the superconducting state."],"supporting_citations":[{"why":"Defines the intertwined SDW/CDW and the Tdw-from-derivative method used throughout the paper.","marker":"[16]"},{"why":"Provides the pressure suppression rate that the authors compare with the Cu substitution rate.","marker":"[34]"},{"why":"Shows the opposite trend for Al substitution, establishing that the suppression is specific to Cu doping.","marker":"[32]"},{"why":"Demonstrates the Hall-number jump near the pseudogap critical point, the analog for carrier delocalization.","marker":"[36]"},{"why":"Shows that Cu doping of TiSe2 suppresses CDW and enhances carrier concentration, a similar chemical route.","marker":"[37]"},{"why":"Reports superconductivity in pressurized La4Ni3O10, the reference state for which the density-wave suppression is a precursor.","marker":"[2]"}],"fun_headline_variants":["Cu doping kills density waves, leaves spin correlations intact","Linear suppression of density waves by Cu, no superconductivity","Charge order disappears, spin order survives under Cu doping","Cu substitution suppresses intertwined order without superconductivity","Density wave death at 14 K per percent Cu, but no superconductivity"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The interpretation relies on the susceptibility kink being a true spin-density-wave signature and on the low-temperature Hall count measuring carriers freed by density-wave melting rather than impurity or band-structure effects.","fun_headline_variants_meta":{"raw":{"variants":["Cu doping kills density waves, leaves spin correlations intact","Linear suppression of density waves by Cu, no superconductivity","Charge order disappears, spin order survives under Cu doping","Cu substitution suppresses intertwined order without superconductivity","Density wave death at 14 K per percent Cu, but no superconductivity"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000234,"raw_usage":{"total_tokens":1510,"prompt_tokens":972,"completion_tokens":538,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":588,"completion_tokens_details":{"reasoning_tokens":457}},"tokens_in":588,"tokens_out":538,"duration_ms":6528,"temperature":1.0,"reasoning_tokens":457,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T18:09:24.384531+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A neutron or muon measurement on La4Ni2.7Cu0.3O10+δ that finds no incommensurate magnetic order and no diffuse spin correlations would falsify the claim of surviving short-range spin correlations; alternatively, detecting a copper-oxide or nickel-oxide impurity phase that accounts for the susceptibility kink, or showing that the Hall carrier density changes strongly with oxygen annealing, would undermine the carrier-delocalization argument.","supporting_citations":[{"cited_title":"Zhang et al., Intertwined density waves in a metallic nickelate, Nat Commun 11, 6003 (2020)","cited_arxiv_id":null,"evidence_quote":"Defines the intertwined SDW/CDW and the Tdw-from-derivative method used throughout the paper."},{"cited_title":"Electron doping of the layered nickelate La$_4$Ni$_3$O$_{10}$ by aluminum substitution: A combined experimental and DFT study","cited_arxiv_id":"2006.12854","evidence_quote":"Shows the opposite trend for Al substitution, establishing that the suppression is specific to Cu doping."},{"cited_title":"Badoux et al., Change of carrier density at the pseudogap critical point of a cuprate superconductor, Nature 531, 210 (2016)","cited_arxiv_id":null,"evidence_quote":"Demonstrates the Hall-number jump near the pseudogap critical point, the analog for carrier delocalization."},{"cited_title":"Morosan, H","cited_arxiv_id":null,"evidence_quote":"Shows that Cu doping of TiSe2 suppresses CDW and enhances carrier concentration, a similar chemical route."},{"cited_title":"Zhang et al., Superconductivity in Trilayer Nickelate La 4 Ni 3 O 10 under Pressure, Phys","cited_arxiv_id":null,"evidence_quote":"Reports superconductivity in pressurized La4Ni3O10, the reference state for which the density-wave suppression is a precursor."}],"review_version":1}