{"id":"df8a8067-808b-4d03-a6f8-10422110d339","arxiv_id":"2608.00942","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":1,"one_line_summary":"Under quasihydrostatic pressure up to 60 GPa, Bi-2223 cuprate shows magnetic signatures consistent with superconductivity up to 190 K, exceeding prior cuprate records.","lead":"A team reports that Bi-2223, a cuprate superconductor, reaches a critical temperature of 190 K when squeezed to 60 GPa in a diamond anvil cell, the highest T_c yet claimed for a cuprate. The claim rests on magnetic susceptibility signals suggesting a second superconducting regime at high hole doping, but the evidence is indirect and lacks error bars.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"190 K point rests on double-modulation phase features that the paper itself flags as overtone-prone, without shown 60 GPa RF/AC corroboration or error bars; quasihydrostaticity at 60 GPa is unverified.","rationale":"The reader's weakest assumption identifies the same broad vulnerability: the 190 K signal might not be a genuine Meissner effect. My review sharpens this by pointing to a specific, self-admitted instrumental risk in the double-modulation technique and the lack of a directly shown 60 GPa RF/AC trace. The paper's own text acknowledges overtone artifacts and stress-gradient effects, which makes the 60 GPa point especially fragile. However, this does not refute the claim; it only means the evidence, as presented, is insufficient to establish a record T_c. The reader's CONDITIONAL verdict is therefore appropriate, and the repository check would either corroborate or undermine the key point.","tokens_in":11492,"tokens_out":5126,"duration_ms":56593,"concrete_test":"From the Zenodo repository, extract the 60 GPa double-modulation and RF traces taken on the same loading and verify that the RF trace shows a reproducible transmission dip within 2-5 K of the double-modulation feature. If the 60 GPa RF dataset is absent, or the dip does not appear, the 190 K point lacks independent Meissner confirmation and should be treated as unverified.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim ('T_c climbs continuously to 190 K at 60 GPa') requires that the feature assigned as T_c in the 20/80 KCl samples at 60 GPa is a bulk Meissner transition, not a background/overtone artifact, and that the sample remains sufficiently quasihydrostatic. The paper's own Methods section lists 'instrumental artifacts are apparent in the recovered signals due to nonlinearities in the circuitry, induced background magnetic response, and the appearance of overtones and oscillations at multiples of the driving frequency,' and Fig. 4a notes that oscillations are instrumental. At 39 GPa the standard AC susceptibility already shows multiple features attributed to stress gradients, and the less-quasihydrostatic 50/50 KCl mixture suppresses T_c above 30 GPa. Yet the 60 GPa point is presented only as a double-modulation phase-angle feature without error bars, sample-to-sample replication, or a directly shown RF/AC trace at that pressure. The RF technique is described as corroborating, but no 60 GPa RF value is reported and RF T_c values are stated to be systematically 2-5 K lower. Thus the record claim currently rests on a single inductive technique at its highest-pressure, least-characterized point, in a regime where the authors themselves document instrumental and hydrostaticity complications.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports measurements of the superconducting critical temperature of Pb-substituted Bi-2223 under quasihydrostatic pressure to 60 GPa, using three inductive methods: AC susceptibility, a double-modulation technique, and RF susceptibility. Below 25 GPa the data reproduce earlier non-monotonic pressure dependencies. The central claim is that above this regime T_c rises continuously to 190 K at 60 GPa, which would be the highest T_c reported for cuprates at any pressure. The authors interpret this as evidence for a second superconducting dome at high hole doping, supported by qualitative DFT-PBE estimates of pressure-induced hole doping and by prior proposals of a Lifshitz transition.","tokens_in":11799,"tokens_out":4274,"duration_ms":47328,"significance":"If substantiated, the claim is important: it would establish a new pressure record for cuprate superconductivity, with direct bearing on the phase diagram of overdoped cuprates and on proposals for a second pairing dome. The paper's strengths include the use of multiple independent probes over most of the pressure range, careful comparison with prior data in different compression media, and a data-availability statement. The DFT calculations are explicitly framed as qualitative. However, the headline 190 K result rests on a single inductive-channel feature at the highest pressure, with no error bars, no shown corroborating technique at that pressure, and unverified quasihydrostaticity. These gaps are load-bearing for the record claim.","major_comments":[{"comment":"The 190 K point rests on the double-modulation phase-angle feature at 60 GPa. The Methods paragraph explicitly acknowledges 'instrumental artifacts are apparent in the recovered signals due to nonlinearities in the circuitry, induced background magnetic response, and the appearance of overtones and oscillations at multiples of the driving frequency,' and the Fig. 4a caption states that 'Oscillations in measurements are instrumental and due to overtones of the driving frequencies.' No error bar, no directly shown |V_mod(T)| trace at 60 GPa, and no RF/AC corroboration at 60 GPa are provided. Given that the RF technique is described as systematically lower by 2-5 K, the reader cannot exclude that the 60 GPa feature is an overtone or background artifact. This issue is central to the abstract's claim.","section":"§III, Fig. 4a; §II.B"},{"comment":"The claim that 20/80 Bi-2223/KCl remains sufficiently quasihydrostatic at 60 GPa is unverified. The paper itself attributes the multiple features at 39 GPa (Fig. 2a) to 'pressure gradients developing across the sample,' and shows that the less-hydrostatic 50/50 mixture suppresses T_c above 30 GPa (Fig. 3). No pressure-medium characterization at 60 GPa (e.g., ruby linewidth, diamond Raman stress signature, or x-ray stress analysis) is reported for the actual sample environment. The possibility that deviatoric stress or sample degradation contributes to or suppresses the observed 60 GPa feature is not excluded.","section":"§III, Figs. 2 and 3; §II.A"},{"comment":"No estimate of uncertainty is given for the 190 K point. The number of independent runs, DAC loads, and sample batches used to establish this point is not stated, and no error bars appear in Fig. 5. In addition, no quantitative Meissner fraction or diamagnetic signal magnitude is reported. For a record claim exceeding all previous cuprate T_c values, a single un-replicated feature without stated measurement uncertainty is insufficient. The authors should provide replicate data and quantify the uncertainty in T_c and pressure, or temper the abstract's categorical statement.","section":"§III, Fig. 5; §IV"}],"minor_comments":[{"comment":"The sentence 'Evidence for critical temperatures exceeding those reported to date for cuprates at ambient and high pressures, the results may be understood...' is grammatically incomplete. It should be rephrased, e.g., 'The results provide evidence for... and may be understood...'","section":"Abstract"},{"comment":"Instrument model numbers are written as 'SRS 860' and 'SRS 844'; the commercial prefixes are 'SR860' and 'SR844.' Please confirm the model designations.","section":"§II.B"},{"comment":"The caption states that 'instrumental noise apparent in the 6 GPa dataset removed at 125 K - 150 K for clarity.' Removing data over such a wide interval can bias the appearance of a transition; please justify this removal or show the raw trace.","section":"Fig. 4b"},{"comment":"The inset legend uses the same green open circles for both the 50/50 data and 'previous data in various media labeled nonhydrostatic.' This is confusing; please distinguish the datasets with distinct symbols or labels.","section":"Fig. 5 inset"},{"comment":"The DFT-PBE estimate n_H ≈ 0.52 is presented as a single value without sensitivity to pseudopotential or k-mesh choices. Since the authors correctly state that DFT-PBE is inadequate for quantitative cuprate electronic structure, this value should be labeled as illustrative, not as a quantitative prediction.","section":"§IV, Fig. 6"}],"recommendation":"major_revision","confidential_remarks":"The central scientific claim is potentially significant but currently under-supported at the exact pressure where it breaks new ground. The manuscript's own methods section and figure captions identify the exact instrumentation artifacts and hydrostaticity concerns that the authors must address. This is not a question of internal inconsistency, but of missing evidence that is feasible to supply: reproduce the 60 GPa point, show the raw double-modulation traces with backgrounds, provide error bars and run counts, attempt RF or direct AC measurement near 60 GPa, and characterize the compression environment. I see no reason to doubt the authors' good faith, and the literature base includes prior work from the same group, but the record claim should be held to a high evidentiary standard."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Short version: this is a careful high-pressure study with a load-bearing weak spot at the very top. The paper extends T_c measurements on Bi-2223 from 40 GPa to 60 GPa and reports 190 K, which would beat the old cuprate record by roughly 26 K. That is a big deal if true. But the 190 K point is exactly where the evidence gets thinnest.\n\nWhat's genuinely good: the low-pressure data agree with Chen et al. and with their own methanol/ethanol runs; the comparison between 20/80 and 50/50 KCl mixtures makes a clean case that hydrostaticity matters; and they used three different probes. They are candid about the known artifacts in the double-modulation technique in Methods, and the DFT section is appropriately hedged as qualitative. The data repository is a real plus.\n\nNow the soft spot, and it's in the right place: the record claim. The 190 K point comes from a single double-modulation phase-angle feature at 60 GPa. No error bars, no replicate runs shown, and no RF trace at that pressure; the RF data are described as systematically 2–5 K lower, but no 60 GPa value is displayed. Meanwhile, at 39 GPa the standard AC susceptibility already shows multiple features that the authors attribute to stress gradients, and the 50/50 mixture kills the T_c rise above 30 GPa. The Methods section explicitly lists overtones and nonlinearities as instrumental artifacts in the recovered signals. So the highest-pressure point sits in the regime where the technique is least reliable and the pressure environment is least characterized. That does not mean the signal is false, but it means the abstract's 'climbs continuously to 190 K' is ahead of the evidence shown.\n\nI'd still send this to a serious referee. The question is important, the experiment is hard, and the authors are not hiding their limitations. The referee should ask for the raw data behind Fig. 4a, a replicate at 60 GPa, and a direct RF or AC sweep at that pressure. Until then, treat 190 K as promising but unverified. I would cite it as 'reported' in a review, but I wouldn't build anything on it yet.","headline":"Bi-2223 at 60 GPa: plausible but unconfirmed 190 K, with the weakest evidence exactly at the record point.","tokens_in":12348,"tokens_out":3548,"would_cite":true,"duration_ms":37411,"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":"The paper claims quasihydrostatic pressure raises the superconducting critical temperature of Bi-2223 to 190 K at 60 GPa, the highest reported for cuprates, by entering a second high-doping superconducting regime.","keywords":["cuprate superconductivity","Bi-2223","high pressure","Meissner effect","diamond anvil cell","overdoped cuprates","second superconducting dome","Lifshitz transition"],"falsifier":"Field-cooled magnetization or magnetic flux imaging of Bi-2223 at 60 GPa in a noble-gas pressure medium (Ne or He) would settle it: if no diamagnetic flux expulsion appears near 190 K, or if x-ray diffraction at 60 GPa shows a structural phase change, decomposition, or strong deviatoric broadening, then the 190 K signal is not a bulk superconducting transition.","tokens_in":11408,"feed_emoji":"🧲","tokens_out":9211,"duration_ms":90864,"temperature":0.7,"pith_summary":"Using three complementary probes of the Meissner effect inside a diamond anvil cell, this paper follows the superconducting transition of the trilayer cuprate Pb0.4Bi1.6Sr2Ca2Cu3O10+δ (Bi-2223) up to 60 GPa. It reports that samples compressed under quasihydrostatic conditions first show the familiar non-monotonic dome in $T_c$ below 25 GPa and then a continuous rise to 190 K at 60 GPa, which the authors take to be the highest critical temperature reported for any cuprate. The proposed explanation is that pressure decouples hole doping from chemical oxygen doping, driving the material into a highly overdoped regime where a Fermi-surface Lifshitz transition supports a second superconducting dome. If correct, this would extend the cuprate phase diagram far beyond the ambient-pressure dome and make pressure a route to higher-$T_c$ superconductivity in this family.","feed_headline":"Pressure lifts a cuprate superconductor to 190 K","feed_subtitle":"Three magnetic probes trace Tc rising past all previous cuprate records into a pressure-driven second dome.","key_machinery":"The load-bearing mechanism is pressure-induced hole doping: compression transfers charge out of the CuO2 planes into the charge-reservoir layers, increasing the hole concentration $n_H$ per plane while oxygen content stays fixed. The paper argues this decoupling lets $n_H$ reach about 0.52 at 60 GPa, driving a Lifshitz transition (the $d_{3z^2-r^2}$ band crossing the Fermi level) and a second superconducting dome. The quasihydrostatic 20/80 Bi-2223/KCl environment is the experimental condition that preserves this state; the double-modulated AC susceptibility is the measurement technique that resolves the 190 K onset.","core_discovery":"In the paper's own terms, the discovery is evidence that Bi-2223 under quasihydrostatic pressure enters a second superconducting regime at high hole doping, with the Meissner onset rising from a minimum near 25 GPa to 190 K at 60 GPa. The claim rests on three detection techniques—AC susceptibility, double-modulated susceptibility, and RF susceptibility—all measuring the onset of magnetic field expulsion. Samples in a more hydrostatic 20/80 Bi-2223/KCl mixture show the rise, while a stiffer 50/50 mixture suppresses $T_c$ above 30 GPa, which the authors attribute to deviatoric stress. DFT calculations using experimentally measured lattice parameters put the effective hole doping near $n_H \\app","pith_inferences":["A direct test that goes beyond the paper: perform field-cooled and zero-field-cooled magnetization on a single crystal of Bi-2223 in a noble-gas medium at 60 GPa; bulk flux expulsion near 190 K would rule out stress-gradient artifacts.","The 20/80 vs 50/50 KCl contrast suggests a tunable experimental knob: varying the KCl fraction at fixed pressure should sweep $T_c$ continuously if non-hydrostatic stress is the suppressor, or leave it unchanged if chemistry or grain size matters.","If the second dome is real, analogous pressure-doping experiments on Bi-2212 and Bi-2201 should reveal similar upturns at higher pressures, since the same Lifshitz argument has been made for those compounds.","The pressure-quench idea proposed in the literature for retaining high $T_c$ at ambient pressure could be transferred to Bi-2223: synthesize in the 190 K state at 60 GPa, then rapidly decompress and test for metastable retention."],"forward_implications":["Cuprate superconductivity is not bounded by the ambient-pressure parabolic dome: pressure can push $T_c$ past 190 K in a trilayer cuprate.","The previously conflicting $T_c(P)$ reports for Bi-2223 are explained as a competition between quasihydrostatic and non-hydrostatic compression environments.","Pressure can substitute for oxygen doping to explore hole concentrations $n_H > 0.3$ that are nearly inaccessible in bulk synthesis.","If a Lifshitz transition is the cause, the high-pressure state should show a change in Fermi-surface topology and pairing symmetry relative to ambient-pressure Bi-2223.","The second-dome picture implies a finite pressure window: $T_c$ may continue rising beyond 60 GPa, or eventually turn over as the dome is crossed."],"supporting_citations":[{"why":"Supplies the previous Tc-vs-pressure curve for Bi-2223 to 40 GPa and the Tc assignment criterion the paper adopts.","marker":"[5]"},{"why":"Gives the pressure-induced Lifshitz transition hypothesis for Bi-2201 and Bi-2212 that this work extends to Bi-2223.","marker":"[7]"},{"why":"Provides the experimental lattice parameters and equation of state used in the DFT estimate of pressure-induced doping.","marker":"[8]"},{"why":"Documents deviatoric-stress suppression of superconductivity, used to explain why non-hydrostatic media show lower Tc.","marker":"[12]"},{"why":"Supplies the double-modulation susceptibility technique used to detect the high-pressure Meissner onset.","marker":"[15]"},{"why":"Supplies the RF susceptibility method used as an independent check on the superconducting onset.","marker":"[16]"},{"why":"Proposes a second superconducting dome at high hole doping in cuprates, the framework for interpreting the 190 K state.","marker":"[17]"},{"why":"Supplies the parabolic Tc-nH relation whose deviation motivates the claim of a distinct high-doping regime.","marker":"[25]"},{"why":"Offers comparison data in less-quasihydrostatic media, supporting the stress-dependent dome shapes the paper reports.","marker":"[40]"}],"fun_headline_variants":["Cuprate superconductivity reaches 190 K under pressure","Pressure reveals new superconducting regime at 190 K","Overdoped cuprate hits 190 K, best yet under pressure","190 K superconductivity in cuprate via pressure overdoping","Cuprate Tc climbs to 190 K in second dome under pressure"],"cache_read_input_tokens":2816,"weakest_assumption_plain":"The whole result depends on the assumption that the 20/80 Bi-2223/KCl mixture stays sufficiently quasihydrostatic at 60 GPa for the 190 K signal to be a genuine bulk Meissner transition rather than an artifact of stress gradients, sample damage, or background; the paper itself notes that at 39 GPa stress gradients begin to split the transition and that the stiffer 50/50 mixture suppresses Tc above 30 GPa.","fun_headline_variants_meta":{"raw":{"variants":["Cuprate superconductivity reaches 190 K under pressure","Pressure reveals new superconducting regime at 190 K","Overdoped cuprate hits 190 K, best yet under pressure","190 K superconductivity in cuprate via pressure overdoping","Cuprate Tc climbs to 190 K in second dome under pressure"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000776,"raw_usage":{"total_tokens":3264,"prompt_tokens":732,"completion_tokens":2532,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":476,"completion_tokens_details":{"reasoning_tokens":2445}},"tokens_in":476,"tokens_out":2532,"duration_ms":18067,"temperature":1.0,"reasoning_tokens":2445,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T00:35:04.674979+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Field-cooled magnetization or magnetic flux imaging of Bi-2223 at 60 GPa in a noble-gas pressure medium (Ne or He) would settle it: if no diamagnetic flux expulsion appears near 190 K, or if x-ray diffraction at 60 GPa shows a structural phase change, decomposition, or strong deviatoric broadening, then the 190 K signal is not a bulk superconducting transition.","supporting_citations":[{"cited_title":"Enhancement of superconductivity by pressure-driven competition in electronic order","cited_arxiv_id":null,"evidence_quote":"Supplies the previous Tc-vs-pressure curve for Bi-2223 to 40 GPa and the Tc assignment criterion the paper adopts."},{"cited_title":"Higher superconducting transition temperature by breaking the universal pressure relation","cited_arxiv_id":null,"evidence_quote":"Gives the pressure-induced Lifshitz transition hypothesis for Bi-2201 and Bi-2212 that this work extends to Bi-2223."},{"cited_title":"Structure and equation of state of Bi2Sr2Can-1CunO2n+4+δ from x-ray diffraction to megabar pressures","cited_arxiv_id":null,"evidence_quote":"Provides the experimental lattice parameters and equation of state used in the DFT estimate of pressure-induced doping."},{"cited_title":"Probing the Meissner effect in single crystals of Bi 2Sr2Ca2Cu3O10+δ via wide-field quantum microscopy under high pressure","cited_arxiv_id":null,"evidence_quote":"Documents deviatoric-stress suppression of superconductivity, used to explain why non-hydrostatic media show lower Tc."},{"cited_title":"Improved techniques for measurement of superconductivity in diamond anvil cells by magnetic susceptibility","cited_arxiv_id":null,"evidence_quote":"Supplies the double-modulation susceptibility technique used to detect the high-pressure Meissner onset."},{"cited_title":"Transmission of Radio-Frequency Waves and Nuclear Magnetic Resonance in Lanthanum Superhydrides","cited_arxiv_id":null,"evidence_quote":"Supplies the RF susceptibility method used as an independent check on the superconducting onset."},{"cited_title":"Enhanced superconductivity in Sr 2CuO4-v","cited_arxiv_id":null,"evidence_quote":"Proposes a second superconducting dome at high hole doping in cuprates, the framework for interpreting the 190 K state."},{"cited_title":"General trends in oxygen stoichiometry effects on T c in Bi and Tl superconductors","cited_arxiv_id":null,"evidence_quote":"Supplies the parabolic Tc-nH relation whose deviation motivates the claim of a distinct high-doping regime."},{"cited_title":"Pressure effect in Bi-2212 and Bi-2223 cuprate superconductor","cited_arxiv_id":null,"evidence_quote":"Offers comparison data in less-quasihydrostatic media, supporting the stress-dependent dome shapes the paper reports."}],"review_version":1}