{"id":"f92e2aaa-c1cc-460f-b081-80ffaac62643","arxiv_id":"2506.14342","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":1,"one_line_summary":"After correcting the Hall number for chain-plane resistivity anisotropy, the planar carrier density in overdoped YBCO rises gradually and only partially recovers the full Fermi volume at p*, disfavoring a pseudogap quantum critical point.","lead":"Researchers measured the Hall effect and resistivity anisotropy in overdoped YBCO crystals at high magnetic fields. They found that after accounting for the copper-oxide chains, the carrier density rises gradually with doping and has not reached the full Fermi volume at the pseudogap critical point p*, arguing against a quantum critical point there.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The gradual-crossover conclusion rests on the unvalidated correction n_pl = n_H(ρ_a/ρ_b)^{-1}; the paper's own Boltzmann check is in a supplement absent from the arXiv version. If that relation is off by ~20-30%, the p≈0.19 data cannot exclude a sharp Fermi-surface reconstruction.","rationale":"The reader's weakest assumption is the same one I would flag: the paper's entire reinterpretation is a multiplicative rescaling of the Hall number by (ρ_a/ρ_b)^{-1}. This is not a peripheral detail; without it, the measured n_H(50 K) data confirm Badoux et al., including a value near 1+p at p≈0.19. With it, n_pl at p* falls below 1+p. Therefore the central claim is only as sound as the parallel-resistor relation. The paper itself labels the interpretation 'critically dependent' on that relation, and the promised Boltzmann-model check is absent from the arXiv submission (Ref. [22] is a placeholder), so the condition for the conclusion is presently unverified. The cited GitHub repository is a positive resource and makes the proposed check feasible. Other noted issues, such as the single 80 K point for S7 and the absence of this group's own data above p*, are secondary; the correction factor is the load-bearing link. If the Boltzmann-code test passes, the CONDITIONAL verdict could be upgraded; if it fails, the no-QCP conclusion should be withdrawn. I therefore keep the reader's CONDITIONAL verdict unchanged.","tokens_in":13020,"tokens_out":13797,"duration_ms":154211,"concrete_test":"Run the published Boltzmann code (github.com/Boltzmann-Y123/Y123) to compute the full conductivity tensor of Y123 in the normal state at T = 50 K for p ≈ 0.19, using the two-plane plus chain Fermi surface with plane-chain hybridization and finite omega_c tau. From the computed sigma tensor, extract n_H and rho_a/rho_b and compare n_H (rho_a/rho_b)^{-1} with the input planar carrier density. Repeat for chain conductivities that produce rho_a/rho_b in the measured range 1.5-2.1. If the inferred n_pl deviates from the input n_pl by more than the quoted ±30% error, the central correction is not robust; if it stays within error in all cases, the gradual-crossover claim is supported.","verdict_should_be":"UNCHANGED","load_bearing_attack":"Section 'Before closing' states that the interpretation is 'critically dependent on the validity of n_pl = n_H(ρ_a/ρ_b)−1.' The relation follows from a parallel-resistor model in which only the CuO2 planes contribute to the Hall conductivity and the chains act as a pure b-axis shunt. This is precisely the assumption that converts the sharp rise in n_H(p) into a gradual n_pl(p) that is a factor ≈1.8 smaller at p*. Applying ρ_a/ρ_b ≈ 1.8 to the p≈0.19 Hall data changes n_pl from near 1+p (full Fermi volume) to a partially recovered value below 1+p. The only quantitative validation cited is a 'minimal Boltzmann transport model' in the Supplemental Material, but the supplement is not included in the arXiv submission (Ref. [22] is a placeholder); the cited GitHub repository alone does not specify the parameter choices and outputs used. If the true relation differs from (ρ_a/ρ_b)^{-1} by 20-30%, for example because the chains have a nonzero Hall conductivity or because plane-chain hybridization invalidates the two-fluid decomposition, the p≈0.19 and p≈0.205 data points could move up to the 1+p line, and the no-QCP conclusion would lose its evidential basis.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports simultaneous high-field measurements of the Hall coefficient and the in-plane resistivity anisotropy in seven detwinned overdoped YBa2Cu3O7-delta crystals (p = 0.16-0.19), and combines them with literature data. Using the relation n_pl = n_H (rho_a/rho_b)^{-1}, the authors extract a planar carrier density n_pl and claim that the sharp rise in n_H(p) observed by Badoux et al. is softened, so that the full Fermi volume n_pl = 1+p is only partially recovered at p*. They argue this disfavors a conventional quantum critical point at p* and reconciles Y123 with Tl2201, Bi2201, and LSCO.","tokens_in":13329,"tokens_out":4149,"duration_ms":45524,"significance":"If the central extraction is valid, the result is significant: it would remove one of the main transport-based pillars for a QCP at p* in Y123 and unify the doping evolution of the carrier density across several cuprate families. The paper has genuine strengths: it measures rho_a/rho_b and R_H on the same crystals, its raw R_H data agree with Badoux et al., and it explicitly acknowledges that the interpretation is critically dependent on the n_pl = n_H (rho_a/rho_b)^{-1} relation. The inclusion of a caveat is commendable, but the validation for that relation is not actually available in the submitted manuscript, which is a load-bearing gap.","major_comments":[{"comment":"The central conclusion that the p to 1+p crossover is gradual and incomplete at p* rests entirely on the relation n_pl = n_H (rho_a/rho_b)^{-1}. The text itself says the interpretation is 'critically dependent' on this relation, and the only quantitative validation is said to be in Supplemental Material Ref. [22]. That supplement is not included in the arXiv submission and Ref. [22] is a placeholder ('Supplemental Material available at tbc.com'). The Boltzmann code repository [64] is cited, but the main text gives no parameter choices, outputs, or a comparison between the model and the measured rho_a/rho_b. Without this validation, the extraction of n_pl is an untested assumption, and the paper's headline claim cannot be assessed.","section":"Before closing / Eq. n_pl = n_H (rho_a/rho_b)^{-1}"},{"comment":"The Badoux et al. data are rescaled by a single anisotropy factor rho_a/rho_b = 1.8, which is the average of the four samples in this work with the most conductive chains. However, the paper itself emphasizes that rho_a/rho_b must be measured on each crystal because it varies strongly with chain disorder; two of the present samples with p = 0.170 have rho_a/rho_b about 1.35. The blue band in Fig. 5b only covers 1.5 <= rho_a/rho_b <= 2.1 and therefore excludes the lower measured values. If the actual chains in the Badoux crystals were less conductive, their n_pl points near p* could lie close to or above the 1+p line, which would erase the claimed partial recovery. A sensitivity analysis using rho_a/rho_b = 1.35, or a justification for why the Badoux crystals should have the highest-chain-conductivity ratio, is needed.","section":"Fig. 5b / section on rho_a/rho_b"},{"comment":"One of the two points closest to p*, sample S7 at p = 0.191, does not have a measured n_H(50 K); because of contact failure the authors use n_H(80 K) from static field data, citing Badoux et al. This point is then plotted and included in the same doping-evolution comparison and in the linear fit in Fig. 5b. Since the claim concerns n_pl(50 K) and the text stresses the low-temperature behavior, the paper should either demonstrate that n_H(80 K) equals n_H(50 K) for this doping on an actual sample in this work, or exclude S7 from the fit and show the conclusion is unchanged.","section":"Fig. 5a/5b and Table I"},{"comment":"The reported uncertainties on n_pl are approximately +/-30%, which is comparable to the difference between the data points near p* and the 1+p line. For example, if n_pl near p* is about 0.8-1.0, a 30% error makes the deviation from 1+p (about 1.19) statistically marginal. The blue shaded region is explicitly described as 'not a definitive boundary', and the text uses phrases such as 'well below 1+p' without a quantitative statistical test. The paper should provide a confidence interval for the fitted n_pl at p* and show whether the lower bound of the data is still below 1+p.","section":"Fig. 5b error bars"}],"minor_comments":[{"comment":"Ref. [22] is listed as 'Supplemental Material available at tbc.com'; this placeholder must be replaced with a proper link or DOI before publication.","section":"Ref. [22]"},{"comment":"The table lists nominal Ca percentages while the text notes EDX shows 5-8% actual Ca in nominal 15% crystals; the reader would benefit from a statement of how the uncertainty in Ca content propagates into the assigned p values.","section":"Table I"},{"comment":"The comparison in Fig. 5c mixes n_pl values extracted at different temperatures for Y123, Tl2201, Bi2201, and LSCO; the caption should state the temperature at which each data set is evaluated.","section":"Fig. 5c"},{"comment":"The statement that n_s(0) = 0.87 is 'around 5 times larger than n_pl' assumes n_pl near 0.16-0.17; it would be clearer to quote the numerical n_pl value used for this comparison.","section":"p. 4, n_s estimate"}],"recommendation":"major_revision","confidential_remarks":"The paper addresses a timely and contested question in cuprate transport, and the experiment itself appears carefully done. My main concern is that the central claim depends on a correction factor whose validation is relegated to a missing supplement, and the treatment of the literature data uses a single hand-chosen anisotropy value. Both are fixable in revision, but they are load-bearing rather than cosmetic. I would not reject the manuscript, but I need to see the supplement and a robustness analysis before endorsing the conclusion."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"First thing to know: the raw experiment is solid, and the headline claim -- that the sharp Hall jump at p* is a chain artifact -- is plausible but rides on a correction whose supporting calculation is not in the arXiv version. Worth refereeing seriously, but the no-QCP conclusion should not be accepted until that supplement is visible.\n\nWhat's new: simultaneous high-field Hall and resistivity-anisotropy data on detwinned overdoped YBCO at 50 K, sample by sample. The n_H values track Badoux et al. well, and the per-crystal rho_a/rho_b data show real variation (1.35 to ~2) with chain quality, which is exactly why the anisotropy has to be measured, not guessed. Applying n_pl = n_H (rho_a/rho_b)^{-1} softens the sharp n_H(p) rise into a gradual crossover that does not terminate at p*. If that correction is right, it removes a central piece of Hall-based evidence for a pseudogap QCP in YBCO and reconciles YBCO with Tl2201 and Bi2201.\n\nThe soft spot is that the correction is the whole game. The parallel-resistor model is plausible and builds on Segawa-Ando, but the paper itself says the interpretation is critically dependent on its validity, and the quantitative validation is a 'minimal Boltzmann transport model' in a supplement that is absent from the arXiv posting (Ref [22] is a placeholder). The GitHub repository is nice, but it does not specify the parameter choices and outputs used. So the key check is uncheckable right now. The doping range also barely crosses p*: two samples at p~0.19, one with n_H(80 K) instead of 50 K, and +/-30% error bars on n_pl. The gradual-crossover conclusion leans on the rescaled Badoux points and a linear fit extrapolated beyond the measured range. If the true relation differs from (rho_a/rho_b)^{-1} by 20-30%, the p~0.19 points could sit back on the 1+p line.\n\nI want to stress that I do not doubt the raw data. The experiment is careful, the comparison with Badoux is honest, and the authors flag the critical assumption explicitly. The issue is the distance between 'consistent with a gradual crossover' and 'disfavors a QCP.' A serious referee should take this paper, but should insist on the supplement and a sensitivity analysis. This is a useful data paper either way.","headline":"Solid new data, but the no-QCP claim rides on a chain-correction whose validation is in a missing supplement.","tokens_in":13865,"tokens_out":4409,"would_cite":true,"duration_ms":44600,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["74.72.-h","74.25.F-","71.18.+y"],"model":"deepseek-v4-flash","headline":"The sharp Hall jump in overdoped YBCO softens once CuO chain conduction is removed, so the pseudogap endpoint may not be a quantum critical point.","keywords":["cuprate superconductors","Hall effect","pseudogap","quantum critical point","YBa2Cu3O7-delta","resistivity anisotropy","Fermi surface","high magnetic fields"],"falsifier":"Quantum oscillation measurements on the same overdoped Y123 crystals at $p \\gtrsim p^*$: if the oscillation-derived Fermi-surface volume already equals $1+p$ holes per CuO$_2$ plane at $p^*$, or any other direct measurement of $n_{\\mathrm{pl}}$ that does not rely on the anisotropy correction returns the full Fermi volume there, the gradual-crossover claim is refuted.","tokens_in":12849,"feed_emoji":"🧲","tokens_out":10043,"duration_ms":90988,"temperature":0.7,"pith_summary":"This paper claims that the sharp rise in the Hall carrier density of overdoped YBa$_2$Cu$_3$O$_{7-\\delta}$ near the putative pseudogap endpoint $p^* \\approx 0.19$ is not the full story: once the conduction of the CuO chains is accounted for, the planar carrier density rises gradually from $p$ at optimal doping toward $1+p$ only near the edge of the superconducting dome. Using pulsed fields up to 67 T, the authors measured the Hall coefficient and the in-plane resistivity anisotropy on the same detwinned crystals and extracted $n_{\\mathrm{pl}} = n_{\\mathrm{H}}(\\rho_a/\\rho_b)^{-1}$. They confirm a previously reported jump in $n_{\\mathrm{H}}$, but find that $n_{\\mathrm{pl}}$ at $p^*$ remains well below the full Fermi volume and shows no feature at $p^*$. If this is right, the popular reading of the Hall jump as evidence for a quantum critical point and Fermi-surface reconstruction at the pseudogap endpoint needs to be abandoned, and overdoped Y123 joins other cuprates in a common gradual crossover.","feed_headline":"Sharp Hall jump in YBCO softens under anisotropy correction","feed_subtitle":"After removing the CuO-chain contribution, the planar carrier density climbs smoothly from p toward 1+p across the overdoped region.","key_machinery":"The key object is the correction $n_{\\mathrm{pl}} = n_{\\mathrm{H}}(\\rho_a/\\rho_b)^{-1}$, derived from a parallel-resistor model of the CuO$_2$ planes shunted by quasi-1D CuO chains; it converts the measured Hall number into an estimate of the actual planar carrier density. The argument is carried by measuring both quantities on the same detwinned crystal at 50 K in pulsed fields up to 67 T, using standard anisotropic resistance extraction, and by checking the correction against a minimal Boltzmann transport model that includes two CuO$_2$ planes per unit cell, chain anisotropy, plane-chain hybridization in $k$-space and finite $\\omega_c\\tau$.","core_discovery":"The central claim is that in overdoped Y123 the $p$ to $1+p$ crossover in the planar carrier density is gradual rather than sharp. The measured $n_{\\mathrm{H}}(50\\,\\mathrm{K})$ does rise sharply near $p^*$ as previously reported, but this rise is largely an effect of the quasi-1D CuO chains that shunt the Hall response; renormalising by the measured anisotropy gives $n_{\\mathrm{pl}} \\approx p$ at optimal doping and $n_{\\mathrm{pl}} \\approx 1+p$ only partially recovered by $p \\approx 0.19$, with the full value reached only toward the end of the superconducting dome near $p \\approx 0.3$. The authors therefore argue that the sharp Hall feature cannot be used as evidence for a conventional quantum critical point at $p^*$ or for a reconstructed Fermi surface, and that the Y123 data are consistent with the extended strange-metal crossover seen in Tl2201, Bi2201 and LSCO. They further show with a minimal Boltzmann transport model that the anisotropy correction is robust against known semiclassical corrections such as plane-chain hybridization and finite cyclotron motion.","pith_inferences":["If the universal gradual crossover is real, other purported signatures of quantum criticality near $p^*$, such as thermodynamic or spectroscopic features tied to the pseudogap endpoint, may need re-reading as smooth crossovers rather than $T=0$ criticality.","The same anisotropy-correction analysis could be applied to published high-field Hall data on other chain-bearing cuprates, such as YBa$_2$Cu$_4$O$_8$, to test whether their extracted planar densities also fall on the common trend.","A sharper test would be to measure $n_{\\mathrm{pl}}$ directly by quantum oscillations in overdoped Y123 near $p^*$; if the oscillation volume already equals $1+p$ there, the gradual crossover would be an artifact of the parallel-resistor correction.","Because the missing carriers track the superfluid density and $T_c$, an experiment that varies chain disorder at fixed doping (via oxygenation) could separate chain-shunting effects from a genuinely reduced planar carrier density."],"forward_implications":["If the gradual crossover is correct, the absence of any feature in $n_{\\mathrm{pl}}$ across $p^*$ removes the main transport evidence for a conventional quantum critical point at the pseudogap endpoint.","The Y123 data fall onto the same quasi-linear $n_{\\mathrm{pl}}(p)$ trend as Tl2201, Bi2201 and LSCO, implying a universal mechanism for carrier recovery across the overdoped strange-metal regime.","At optimal doping $n_{\\mathrm{pl}} \\approx p$, several times smaller than the estimated superfluid density, so a substantial part of the superconducting condensate must come from carriers that do not contribute to the normal-state Hall response.","The full Fermi volume is only recovered near the end of the superconducting dome, meaning the 'missing' holes persist through most of the overdoped region and correlate with $T_c$ and the low-temperature $T$-linear resistivity.","The apparent sharp rise in Nd-LSCO is likely dominated by the Lifshitz transition, where electron-like and hole-like Fermi-surface sections contribute opposite-sign Hall terms, rather than by pseudogap closure."],"supporting_citations":[{"why":"Supplies the original sharp rise in $n_{\\mathrm{H}}(50\\,\\mathrm{K})$ near $p^*$ that this paper reinterprets with the anisotropy correction.","marker":"[10]"},{"why":"Provides the parallel-resistor model from which the correction $n_{\\mathrm{pl}}=n_{\\mathrm{H}}(\\rho_a/\\rho_b)^{-1}$ is derived.","marker":"[23]"},{"why":"Establishes the strong doping and oxygenation dependence of the resistivity anisotropy and chain conduction in Y123.","marker":"[25]"},{"why":"Supplies the planar carrier density data for Tl2201 and Bi2201 that the Y123 results are compared with to infer a universal crossover.","marker":"[9]"},{"why":"Gives the empirical relation between $T_c$ and hole doping $p$ used to assign doping levels to each crystal.","marker":"[27]"},{"why":"Provides the anisotropic resistance extraction method used to obtain $\\rho_a$ and $\\rho_b$ from the contact configuration.","marker":"[29]"},{"why":"Band-structure calculations for Y123 used as input to the minimal Boltzmann model that checks the validity of the anisotropy correction.","marker":"[51]"}],"fun_headline_variants":["Chains, not Fermi surface, drive sharp Hall jump in YBCO","Overdoped YBCO shows gradual carrier-density crossover","Sharp Hall rise in YBCO is a chain artifact","Planar carrier density climbs smoothly from p to 1+p in YBCO","Anisotropy correction blunts Hall feature in YBCO"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The conclusion rests entirely on the validity of $n_{\\mathrm{pl}} = n_{\\mathrm{H}}(\\rho_a/\\rho_b)^{-1}$; if plane-chain hybridization, incoherent conduction, or a Hall contribution not tied to $\\rho_a/\\rho_b$ breaks the parallel-resistor picture, the extracted planar density and the gradual crossover would change.","fun_headline_variants_meta":{"raw":{"variants":["Chains, not Fermi surface, drive sharp Hall jump in YBCO","Overdoped YBCO shows gradual carrier-density crossover","Sharp Hall rise in YBCO is a chain artifact","Planar carrier density climbs smoothly from p to 1+p in YBCO","Anisotropy correction blunts Hall feature in YBCO"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000483,"raw_usage":{"total_tokens":2466,"prompt_tokens":1105,"completion_tokens":1361,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":721,"completion_tokens_details":{"reasoning_tokens":1270}},"tokens_in":721,"tokens_out":1361,"duration_ms":12706,"temperature":1.0,"reasoning_tokens":1270,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-07T00:17:58.278272+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Quantum oscillation measurements on the same overdoped Y123 crystals at $p \\gtrsim p^*$: if the oscillation-derived Fermi-surface volume already equals $1+p$ holes per CuO$_2$ plane at $p^*$, or any other direct measurement of $n_{\\mathrm{pl}}$ that does not rely on the anisotropy correction returns the full Fermi volume there, the gradual-crossover claim is refuted.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the original sharp rise in $n_{\\mathrm{H}}(50\\,\\mathrm{K})$ near $p^*$ that this paper reinterprets with the anisotropy correction."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the parallel-resistor model from which the correction $n_{\\mathrm{pl}}=n_{\\mathrm{H}}(\\rho_a/\\rho_b)^{-1}$ is derived."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Establishes the strong doping and oxygenation dependence of the resistivity anisotropy and chain conduction in Y123."},{"cited_title":"Ayres, M","cited_arxiv_id":null,"evidence_quote":"Gives the empirical relation between $T_c$ and hole doping $p$ used to assign doping levels to each crystal."},{"cited_title":"Segawa and Y","cited_arxiv_id":null,"evidence_quote":"Provides the anisotropic resistance extraction method used to obtain $\\rho_a$ and $\\rho_b$ from the contact configuration."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Band-structure calculations for Y123 used as input to the minimal Boltzmann model that checks the validity of the anisotropy correction."}],"review_version":1}