{"id":"ba879fb7-fd21-40b5-a609-a9aa500c1f75","arxiv_id":"2512.16423","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"Hall measurements on Pr-substituted YBCO show the same sign-reversing Hall coefficient as pure YBCO, implying charge-order-driven Fermi-surface reconstruction and matched phase diagrams across the two doping routes.","lead":"By measuring how electrons are deflected in a magnetic field, this paper finds that Pr-substituted YBCO — a disordered cousin of a key high-temperature superconductor — shows the same Fermi-surface reconstruction signature as pure YBCO, signaling the same type of charge order. The result matters because it suggests that the in-plane hole count, not the specific way it is achieved, governs the electronic orders in these cuprate superconductors.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The Hall sign change is attributed to 2D charge-order Fermi-surface reconstruction, but this hinges on the untested assumption that the ~30 Å correlations seen in thin films grow under 65 T; if they do not, the sign change could have another origin.","rationale":"The experimental work is competently presented: six crystals, duplicate samples, two field polarities for proper antisymmetrization, and a coherent doping progression of the Hall response. The authors are also appropriately cautious in places, using 'we propose' and 'we speculate.' However, the central claim that the data 'indicate the presence of 2D charge order' depends on an inference that is much less secure than the data themselves. The paper has no direct probe of the Fermi surface (quantum oscillations, Seebeck, ARPES) on these bulk crystals, and no x-ray measurement of charge correlations on the measured crystals. The only CO evidence for Pr-YBCO is from thin films with a short correlation length, and the authors rely on field-induced growth of that correlation length—an assumption they state rather than test. In YBCO, field-induced 3D CO is directly observed and reaches ξ≈200 Å; in Pr-YBCO, even the existence of 3D CO is disputed (ref [13] interprets the integer-L peak as a superlattice reflection). This makes the assumed high-field growth more fragile than the reader's summary alone suggests. A secondary weakness is the use of Tc as a proxy for hole doping when comparing phase diagrams, which builds some apparent symmetry into the comparison; I have not made this the primary concern because the central charge-order claim would fail regardless. The correct evaluation is conditional acceptance: the data support a Fermi-surface reconstruction of some kind, but the specific identification with 2D charge order remains a reasonable hypothesis pending a direct field-dependent structural or Fermi-surface probe. My concern does not change the reader's CONDITIONAL verdict; it sharpens the specific test that would confirm or refute it.","tokens_in":14674,"tokens_out":6887,"duration_ms":70497,"concrete_test":"Perform field-dependent resonant x-ray scattering on the same bulk Pr-YBCO crystals (x≈0.2–0.35) in magnetic fields up to ~30 T, following the YBCO measurements of refs [42,46], and extract the in-plane charge-order correlation length ξ(B) at low temperature. If ξ at high field remains at the thin-film value (25–30 Å) with no field-induced growth, the assumption that short-range 2D correlations reconstruct the Fermi surface is falsified, and the Hall sign change would need an alternative explanation.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The load-bearing step is not the Hall measurement itself but the interpretation of the low-T sign change as an electron pocket produced by biaxial 2D charge order. The only direct charge-order evidence in this system is thin-film REXS/GIXD with in-plane correlation length 25–30 Å (refs [12,13] discussed in §V.2); no x-ray or quantum-oscillation data exist for the bulk crystals measured here. The authors explicitly bridge this with an untested assumption: §V.2 says 'we cannot exclude that it increases under a strong magnetic field, as it is the case in YBCO', and §V.4 says 'If we assume that the correlation length grows at high magnetic field in order to reconstruct the FS...'. This assumption is load-bearing because in YBCO the 2D CO correlation length is ~60–100 Å and even there ref [54] argues such short correlations are insufficient to explain quantum oscillations; a threefold-smaller ξ in Pr-YBCO is far more marginal. If the correlations do not strengthen under field, the negative Hall coefficient could instead reflect reconstruction by an antiferromagnetic-type order—the scenario the paper itself invokes for x≥0.4 (§IV)—or a field-dependent multiband/transport effect. In that case the abstract's 'indicating the presence of 2D charge order' is not supported, and the claimed symmetry with YBCO weakens. The paper's own admission that the characteristic CO–SC competition is absent (no Tc plateau, no Hc2 suppression; Fig. 5, §IV) is a self-flagged challenge to the reconstruction scenario rather than a resolved issue.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports high-field Hall-effect measurements on Pr_xY_{1-x}Ba2Cu3O7 crystals (x=0.2–0.45, Tc≈32–70 K). It finds a sign change of RH from positive to negative at low temperature for x=0.2 and 0.35, with T0 decreasing with decreasing Tc; for x=0.4 and 0.45 RH remains positive. By analogy with YBCO, the authors attribute this to a Fermi-surface reconstruction by 2D charge order and conclude the Pr-YBCO and YBCO phase diagrams are symmetric when disorder and different doping mechanisms are considered.","tokens_in":1570,"tokens_out":2362,"duration_ms":106061,"significance":"If the interpretation holds, the result extends charge-order-induced Fermi-surface reconstruction to a bulk cuprate with strongly suppressed correlation length and a distinct doping route, supporting the view that in-plane hole concentration controls electronic orders. The experimental core—two-polarity antisymmetrized Hall data across a doping series—is well executed, and the comparison with YBCO, Zn-YBCO, and Hg1201 is informative. The paper is transparent about its main assumption (field-induced growth of correlation length) and considers the AFM alternative. Its value lies in the dataset and the explicit formulation of a testable assumption, but the abstract's causal claim exceeds the direct evidence.","major_comments":[{"comment":"The attribution of the negative low-T RH to 2D charge-order-induced FSR rests on an explicit, untested assumption. §V.2 states 'we cannot exclude that it increases under a strong magnetic field' and §V.4 says 'If we assume that the correlation length grows...'. The only CO evidence is thin-film REXS/GIXD with ξ ≈ 25–30 Å (refs [12,13]); no x-ray or QO data exist for the bulk crystals measured here. If ξ does not grow under field, the sign change could reflect the AFM-type FSR invoked for x ≥ 0.4 (§IV). The abstract's 'indicating the presence of 2D charge order' is therefore not supported; the conclusion should be softened or supplemented with a quantitative estimate.","section":"§V.2, §V.4, Abstract"},{"comment":"The 'decidedly symmetric' phase-diagram claim is partly built into the comparison because Pr-YBCO samples are not assigned a hole doping p. §II says 'it is not possible to label our samples with a specific hole doping p', yet Fig. 6 plots T0 versus 'doping p' without explaining the Tc-to-p conversion. Since Pr suppresses Tc through pair-breaking and disorder as well as carrier depletion, equal Tc does not imply equal p. The conclusion should be supported by an explicit calibration or restricted to a Tc-based qualitative comparison.","section":"§II, Fig. 6, §VI"},{"comment":"The absence of canonical CO–SC competition is acknowledged in §IV, and Fig. 5 shows no Tc plateau or Hc2 dip. The response that disorder smears the competition is plausible but not demonstrated; Hg1201 with similar ξ still shows a Tc anomaly. The pressure evidence (ref [63]) is indirect. This part should be framed as a prediction for future x-ray/thermodynamic tests, not as an established consequence.","section":"§IV, Fig. 5, §V.4"}],"minor_comments":[{"comment":"T0 values lack uncertainties; add estimates from duplicate samples and field/temperature resolution.","section":"Fig. 2/3"},{"comment":"2D CO correlation length in YBCO is given as 'up to 60 Å' and later '80–100 Å'; reconcile.","section":"§I vs §V.2"},{"comment":"Text says six crystals but figures show four; clarify that duplicates gave identical results.","section":"Table I"},{"comment":"Wording suggests direct charge-order measurement; suggest 'signatures of charge-order-induced Fermi-surface reconstruction'.","section":"Title/Abstract"}],"recommendation":"major_revision","confidential_remarks":"This is a well-executed transport study with a useful dataset, but the central claim in the abstract overreaches the evidence. Major revision is appropriate: the authors should recalibrate the strength of their conclusion, add a p-calibration if possible, and explicitly discuss the AFM-reconstruction alternative. No requirement for new x-ray data on these crystals, but the current statement 'indicating the presence of 2D charge order' should be softened to 'consistent with'."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"New high-field Hall data on bulk Pr-YBCO crystals show a doping-dependent sign change in R_H for x=0.2 and 0.35 that looks like YBCO's T0(p), and that is the real news. This is a clean, careful transport study: six crystals, two field polarities, standard antisymmetrization, and a frank comparison with YBCO, Zn-YBCO, and Hg1201. The authors also do something refreshing: they state the major caveat—the absence of the usual CO–SC competition—and treat it as a challenge rather than hiding it.\n\nThe soft spot is the interpretive bridge. The sign change is attributed to 2D charge order, but the only direct evidence of 2D CO in this system is thin-film REXS with a 25–30 Å correlation length, and there is no x-ray or quantum oscillations on these bulk crystals. The paper explicitly assumes the correlation length grows under a 65 T field (a reasonable analogy to YBCO, but an assumption). If that fails, the negative Hall coefficient could have another origin, including the AFM-type reconstruction the authors themselves invoke for x≥0.4. So the abstract's 'indicating the presence of 2D charge order' overstates what the data show; 'consistent with' would be more accurate.\n\nA smaller issue is the 'decidedly symmetric phase diagram' claim. Since the authors assign hole doping by mapping Tc to p using YBCO, part of the symmetry is baked into the axis choice. That's a legitimate way to present the data, but it undercuts the strength of the claim.\n\nI also would have liked error bars or raw data in the figures, though the duplicate samples help.\n\nAll in all, this is a solid experimental paper with a new, usable data set. The interpretation is plausible but not established, and the authors say so. It deserves a serious referee. I'd send it to review; the main requests would be a more careful abstract, a discussion of the doping-axis circularity, and ideally a field-dependent x-ray or QO experiment to test the load-bearing assumption.","headline":"New high-field Hall data show a YBCO-like sign change in Pr-YBCO, but the charge-order attribution rests on an untested field-growth assumption; worth refereeing.","tokens_in":15668,"tokens_out":3198,"would_cite":true,"duration_ms":31070,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Pr-substituted YBCO, a more disordered cousin of YBCO with a different doping route, shows the same low-temperature Hall-effect sign change that in pure YBCO signals Fermi-surface reconstruction by two-dimensional charge order—evidence that","keywords":["cuprate superconductors","charge order","Fermi surface reconstruction","Hall effect","Pr-YBCO","high magnetic fields","underdoped","phase diagram"],"falsifier":"Measure quantum oscillations in a Pr-YBCO crystal with x = 0.2 or 0.35 at fields above the Hall sign change: observation of a low-frequency oscillation from a small electron pocket would support the charge-order-reconstruction claim, while its absence (or a hole-like pocket) would weaken it. Alternatively, resonant x-ray scattering on the same bulk crystals under high magnetic field could check whether the 2D charge-order correlation length grows from ~25-30 Å toward the ~80-100 Å scale that is associated with Fermi-surface reconstruction in YBCO.","tokens_in":14399,"feed_emoji":"🧲","tokens_out":5905,"duration_ms":52852,"temperature":0.7,"pith_summary":"The paper tries to show that Pr-substituted YBCO, despite extra disorder and a different doping mechanism, hosts the same two-dimensional charge order and Fermi-surface reconstruction that are hallmarks of underdoped pure YBCO. It reports that the Hall coefficient of Pr-YBCO crystals changes sign at low temperature for higher-Tc samples (Pr content x = 0.2 and 0.35), with the sign-change temperature T0 falling as Tc falls, matching YBCO's behavior as hole doping varies. For lower-Tc samples (x = 0.4 and 0.45), the Hall coefficient stays positive, again like YBCO near the antiferromagnetic phase. The authors conclude that the phase diagrams of Pr-YBCO and YBCO are 'decidedly symmetric' and that the in-plane hole concentration, not the doping route, governs the electronic orders. A reader should care because the result extends charge-order physics to a more disordered, differently doped cuprate and sharpens the question of how much correlation length is needed to reconstruct a Fermi surface.","feed_headline":"Hall sign flip exposes charge order in Pr-doped YBCO","feed_subtitle":"High-field Hall data mirror YBCO's electron-pocket signature, pointing to plane hole density as the control knob.","key_machinery":"The central observable is the Hall coefficient RH(T) measured in pulsed fields up to 65 T, and in particular the temperature T0 at which it changes sign. In the paper's interpretation, a sign change from positive to negative signals a Fermi-surface reconstruction in which a biaxial two-dimensional charge order with wavevectors (Qx,0) and (0,Qy) folds the large hole-like Fermi surface into small electron-like pockets at the nodes, giving a negative Hall response at low temperature. The comparison quantity is the same T0-versus-doping curve in pure YBCO, used as a fingerprint of charge-order-induced reconstruction. The short correlation length of the charge order in Pr-YBCO is the key tension","core_discovery":"The central claim is that a temperature-dependent sign change in the Hall coefficient RH of Pr-YBCO at high magnetic fields (up to 65 T) is a signature of Fermi-surface reconstruction driven by two-dimensional charge order. For x = 0.2 and 0.35, RH falls sharply below ~100 K and crosses zero at a temperature T0 that decreases with increasing Pr content; for x = 0.4 and 0.45, RH remains positive. This pattern mirrors the doping dependence of RH in pure YBCO, where the negative low-temperature Hall effect is attributed to an electron pocket produced by biaxial charge order. The paper also finds that Pr-YBCO lacks the pronounced competition between charge order and superconductivity seen in YBC","pith_inferences":["If the charge-order attribution holds, an immediate extension is that short-range correlations can reconstruct a Fermi surface in a bulk crystal once a magnetic field stiffens them; high-field x-ray scattering on bulk Pr-YBCO crystals would test this directly.","The claimed phase-diagram symmetry suggests that other isovalent or aliovalent substitutions that remove plane holes without changing the chain reservoir should reproduce the same T0(p) curve, giving a simple experimental fingerprint for future substitution studies.","The absence of an Hirr dip in Pr-YBCO could also be interpreted as the charge order being weaker or more fluctuating than in YBCO; if so, the lack of competition is not solely a disorder effect, a distinction that further transport or thermodynamic measurements on cleaner Pr-YBCO could resolve.","Should future ARPES on Pr-YBCO find the reconstructed electron pocket, that would confirm the Fermi-surface reconstruction mechanism directly rather than by Hall-effect analogy."],"forward_implications":["Underdoped Pr-YBCO should exhibit a small electron pocket in quantum oscillation experiments at high field, analogous to the pocket seen in YBCO and Hg-based cuprates.","The similarity of the T0(p) curves implies that the charge-order instability and the pseudogap scale in these cuprates are controlled by the plane hole density rather than by details of the charge reservoir.","Disorder and short correlation length suppress the competition between charge order and superconductivity, explaining the absence of a Tc plateau and an Hirr dip in Pr-YBCO.","The field may enhance the charge-order correlation length in Pr-YBCO, as it does in YBCO; this is a testable prediction.","The x >= 0.4 samples, with positive RH at all temperatures, are consistent with an antiferromagnetic reconstruction rather than charge-order reconstruction, preserving the YBCO analogy."],"fun_headline_variants":["Pr-YBCO Hall data reveal charge order like pure YBCO","High-field Hall effect uncovers charge order in Pr-doped YBCO","Charge order in Pr-YBCO seen via Hall sign flip","Doping mechanism differs but charge order persists in Pr-YBCO","Plane hole density governs electronic orders in Pr-YBCO"],"cache_read_input_tokens":2304,"weakest_assumption_plain":"The argument rests on the assumption that the short-range two-dimensional charge correlations seen in Pr-YBCO thin films persist in the bulk crystals and grow enough under the 65 T field to reconstruct the Fermi surface; if they do not, the Hall sign change could have a different origin, such as antiferromagnetic reconstruction.","fun_headline_variants_meta":{"raw":{"variants":["Pr-YBCO Hall data reveal charge order like pure YBCO","High-field Hall effect uncovers charge order in Pr-doped YBCO","Charge order in Pr-YBCO seen via Hall sign flip","Doping mechanism differs but charge order persists in Pr-YBCO","Plane hole density governs electronic orders in Pr-YBCO"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000539,"raw_usage":{"total_tokens":2416,"prompt_tokens":730,"completion_tokens":1686,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":474,"completion_tokens_details":{"reasoning_tokens":1605}},"tokens_in":474,"tokens_out":1686,"duration_ms":10038,"temperature":1.0,"reasoning_tokens":1605,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-03T15:32:24.700214+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure quantum oscillations in a Pr-YBCO crystal with x = 0.2 or 0.35 at fields above the Hall sign change: observation of a low-frequency oscillation from a small electron pocket would support the charge-order-reconstruction claim, while its absence (or a hole-like pocket) would weaken it. Alternatively, resonant x-ray scattering on the same bulk crystals under high magnetic field could check whether the 2D charge-order correlation length grows from ~25-30 Å toward the ~80-100 Å scale that is associated with Fermi-surface reconstruction in YBCO.","supporting_citations":[],"review_version":1}