{"id":"d7b33a46-1f87-4da1-b8ba-5b461e034e99","arxiv_id":"2607.16684","paper_version":1,"verdict":"UNVERDICTED","confidence":"UNKNOWN","novelty_score":7.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"Stoichiometric uncapped PrNiO2 shows zero resistance and diamagnetism, defining a narrow superconducting regime at the parent limit that is separated from the known doped dome.","lead":"This paper reports that pristine, undoped PrNiO2 films can superconduct on their own, without the chemical substitutions previously thought necessary. If correct, the finding redraws the nickelate phase diagram as two disconnected superconducting regions rather than one cuprate-like dome.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Unverified oxygen/hydrogen stoichiometry leaves the 'pristine parent' claim unsupported; a direct composition measurement is needed.","rationale":"The reader's weakest assumption is precisely the stoichiometry of the films. My stress-test confirms this as the single most load-bearing point: the paper's headline claim of intrinsic superconductivity in the parent compound depends on the films being exactly PrNiO2. The available evidence (flux ratio, low resistivity, ARPES) is necessary but not sufficient; ARPES is surface-sensitive and does not rule out bulk O vacancies or H. The buffer experiment rules out the substrate interface but not bulk non-stoichiometry. The paper's own sensitivity to cation ratio (Fig. 1b) makes the absence of a direct composition measurement a real gap. A conditional verdict is appropriate: accept if the proposed RBS/ERDA/SIMS check confirms stoichiometry, otherwise the central claim must be revised. This is an honest, targeted concern, not a rejection.","tokens_in":11591,"tokens_out":11974,"duration_ms":132791,"concrete_test":"Perform RBS (for cation and oxygen ratios) and ERDA/SIMS (for hydrogen) on the same 20-uc PrNiO2 films that show Tc0≈7 K and diamagnetic TDO shift. If Pr:Ni = 1.00±0.01, O = 2.00±0.02, and H is below detection, the 'pristine stoichiometric' premise is confirmed; if O deviates ≥2% or H is found, the phase diagram and superconductor identity need re-evaluation.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The central claim requires that the superconducting films are exactly PrNiO2 with no oxygen non-stoichiometry, residual hydrogen, or unintended carrier doping. The only evidence is Pr/Ni flux tuning (Fig. 1b), a low normal-state resistivity, and ARPES showing p≈0.09. None of these quantifies oxygen or hydrogen. Because infinite-layer nickelates are synthesized via topotactic reduction, oxygen vacancies and H intercalation are known hazards. Fig. 1b itself shows that a 2% cation ratio deviation destroys the zero-resistance state, so the films are extremely sensitive to composition; yet the paper provides no RBS, STEM-EELS, or SIMS on the actual superconducting films. Without such a measurement, the 'stoichiometric' label is an assertion, and the doping axis of Fig. 4a (and the 'within 3%' boundary) could be offset by an unknown amount. This is the load-bearing foundation: if the films are PrNiO2−δ or contain H, the claim of intrinsic superconductivity at the parent limit collapses.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports zero resistance and a TDO-detected diamagnetic response in uncapped, nominally stoichiometric 20-uc PrNiO2 films grown on SrTiO3, and argues that this superconductivity is intrinsic to the parent compound rather than to interfacial or capping effects. The authors support this with a Pr/Ni flux-ratio optimization, a Ca-doped spacer-layer control, reproducibility across eight films, and ARPES/Hall data indicating a self-doped parent electronic structure with p≈0.09. They further show that dilute Sr or Ca substitution (x=0.02–0.05) suppresses superconductivity, while isovalent La substitution preserves it, and they construct a phase diagram with a narrow superconducting regime near the parent limit separated from the previously known hole-doped dome by a non-superconducting region. The paper also reports a large upper-critical-field anisotropy for the near-parent state and uses GL analysis to extract coherence length and effective superconducting layer thickness.","tokens_in":11837,"tokens_out":4923,"duration_ms":55507,"significance":"If the central claims hold, this is a major result: it would establish superconductivity in pristine, uncapped infinite-layer nickelates without divalent cation substitution, and it would challenge the single-dome cuprate-like phase diagram by introducing a second, disconnected superconducting regime. The paper's strengths include direct observation of the two canonical superconductivity hallmarks (zero resistance and diamagnetism), a sensible control experiment inserting a non-superconducting spacer layer, reproducible observation across eight films, and combined ARPES/Hall characterization of the parent state. These are concrete, falsifiable observations and the buffer-layer control is well designed. However, the interpretation as an intrinsic, stoichiometric parent-phase phenomenon and the quantitative doping axis of the phase diagram rest on assumptions that the present data do not fully support, as detailed below.","major_comments":[{"comment":"The central claim that the superconducting films are stoichiometric PrNiO2 rests on Pr/Ni flux-ratio tuning and low normal-state resistivity. No direct composition measurement—RBS, SIMS, STEM-EELS, or oxygen-content analysis—is reported for the actual superconducting films. Infinite-layer nickelates are synthesized via topotactic reduction, where oxygen vacancies and hydrogen intercalation are known hazards. The extreme sensitivity shown in Fig. 1b (a 2% cation-ratio deviation destroys the zero-resistance state) underscores how composition-sensitive the synthesis window is, yet it does not quantify anion stoichiometry. If these films are PrNiO2−δ or contain residual H, the labels 'pristine', 'parent', and 'without cation substitution' are not established, and the disconnected-regime interpretation loses its foundation. Hall/ARPES showing p≈0.09 does not exclude compensating oxygen vacanc","section":"Intrinsic superconductivity; Fig. 1b"},{"comment":"The phase diagram's horizontal axis is constructed assuming one hole per substituted Sr/Ca cation (p = x for the lightly doped films) plus the ARPES-derived p≈0.09 for the parent. No Hall or ARPES Luttinger-volume calibration is shown for the x=0.01–0.05 films that define the suppression boundary; the only ARPES on a doped film is x=0.05 (Fig. 3c,d), and even there the increase in hole doping is estimated from an enlarged α pocket rather than from a direct Hall measurement on that composition. If Sr/Ca incorporation is not exactly 100% effective, or if there is charge compensation, the 'within 3%' boundary and the apparent gap between the two superconducting regimes could shift substantially. Per-sample Hall coefficients (or ARPES-determined Luttinger volumes) for the lightly doped films are needed to anchor the doping axis.","section":"A distinct superconducting regime; Fig. 4a"},{"comment":"A key part of the disconnected-regime claim is the absence of superconductivity in x=0.02–0.05 Sr/Ca films. This is negative evidence from a small number of samples, and the situation is delicate: x=0.01 Sr still reaches zero resistance near 2 K, while x=0.02 shows only a partial drop and x=0.03 is insulating. The authors argue against a disorder/quality explanation using stoichiometry optimization and comparable MDC linewidths for x=0.05, but no diamagnetic (TDO) or high-field transport data are shown for the non-superconducting compositions, and the weakly insulating behavior could also arise from cation disorder, oxygen loss during reduction, or nanoscale phase separation. To make the 'true gap' robust, please show more than one or two batches per composition, include TDO or high-field checks for at least one non-superconducting doped film, and provide structural/compositional metrics","section":"Contrasting effects of isovalent and divalent substitution; Fig. 2e,f"},{"comment":"The claimed phenomenological distinction based on upper-critical-field anisotropy uses γ≈68, with Hc2 for H//ab reaching 35 T only at T/Tc≈0.6—not at T_c,50%—so H_ab,c2,50% is not directly measured. The GL analysis yielding ξ_ab(0)=6.23 nm and d_sc=3.56 nm involves fitting parameters including effective superconducting layer thickness, and the manuscript itself concedes the thickness 'is not a precise microscopic thickness.' As written, this section supports but does not independently establish the 'more two-dimensional' distinction. Please report the full fitting procedure, error bars, and sensitivity of γ, ξ_ab(0), and d_sc to the chosen GL model and data range; if H//ab cannot reach the 50% criterion, say so explicitly and discuss how the anisotropy value is obtained.","section":"A distinct superconducting regime; Fig. 4b"}],"minor_comments":[{"comment":"The caption says fields are '(c) in the ab plane and (d) parallel to the ab plane,' which appears to be a typo: one of these should be 'perpendicular to the ab plane.' The text in the main body similarly needs correction for clarity.","section":"Figure 1 caption"},{"comment":"The transition-temperature notation is inconsistent: T_c^90%, T_c0, T_c,50%, and T_c,50% are used without a single defining statement. Please define all once in the text or Methods and use consistently.","section":"Notation, Figs. 1 and 4"},{"comment":"The phrase 'as a function of strong sweeping temperatures' is unclear; probably 'as a function of temperature at various fixed magnetic fields.' Please rewrite.","section":"Figure 1 caption"}],"recommendation":"major_revision","confidential_remarks":"This is a high-impact claim that will attract close scrutiny. The visible transport and ARPES data are internally consistent, and the spacer-layer control is a good idea, but the missing composition measurement and the uncalibrated doping axis are load-bearing. If the authors can add direct composition/oxygen/hydrogen quantification and per-sample doping calibration, the paper could become a very strong contribution. I see no citation or scope problems; the main issue is evidentiary. Major revision is appropriate."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague,\n\nHere's my read of arXiv:2607.16684. The headline claim is genuinely new: zero resistance and a diamagnetic TDO shift in uncapped, nominally stoichiometric PrNiO2, repeated across eight films, with a buffer-layer control that makes an interfacial origin unlikely. If the samples are what the authors say they are, this is the first clean demonstration of intrinsic superconductivity in the undoped infinite-layer nickelate parent, and it deserves attention.\n\nThe paper does a lot right. The growth optimization is carefully motivated—off-stoichiometric films lose the transition, which is a sensible quality indicator. The isovalent La substitution experiment is a good control for chemistry-versus-doping. The ARPES and Hall data consistently place the superconducting films near the self-doped p≈0.09 parent state, which is consistent with the picture. The MDC linewidth comparison is a reasonable way to argue that disorder alone doesn't explain the rapid suppression upon Ca substitution. The citation practice is fair: they cite the prior parent-signature work and are explicit that zero resistance and diamagnetism were missing.\n\nThe soft spots are mostly about what is asserted rather than measured. First, the 'stoichiometric' label. The only evidence is Pr/Ni flux tuning plus low resistivity. There is no RBS, STEM-EELS, or SIMS for oxygen or hydrogen on the actual superconducting films. Given the topotactic reduction route and the known sensitivity of these films, this is a real gap. The stress-test note is not a straw man—it targets the load-bearing claim. Second, the doping axis in Fig. 4a assumes each Sr/Ca contributes one hole, with no per-sample Hall or ARPES calibration for the low-doping films. The 'within 3%' boundary and the 'non-superconducting region' rest on non-observation in a handful of compositions, so the 'disconnected' part of the phase diagram is weaker than the parent superconductivity itself. Third, the Hc2 anisotropy and dsc estimate come from a Ginzburg-Landau analysis with parameters not fully derived in the visible text; this is a minor issue, but it should be checked.\n\nOn balance, the central observation—zero resistance and diamagnetism in uncapped PrNiO2—is plausible and well-controlled within the text, though I can't authenticate the wet-lab data. The disconnected-dome interpretation is interesting but provisional until the stoichiometry and doping calibration are nailed down.\n\nThis paper deserves a serious referee: a strong experimentalist who can judge the growth and characterization, plus someone who knows the nickelate phase diagram literature. I'd bring it to a reading group and cite it as a reported parent-phase SC claim, with the caveat about stoichiometry.\n\nRecommendation: send to peer review; if the composition data are added and the doping axis is justified, this could be a major result.","headline":"A potentially major result—zero resistance and diamagnetism in uncapped, nominally stoichiometric PrNiO2—but the stoichiometry and doping-axis assumptions need direct measurement before the disconnected-dome phase diagram can be trusted.","tokens_in":12377,"tokens_out":2290,"would_cite":true,"duration_ms":24484,"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":"Pristine, undoped PrNiO2 is an intrinsic superconductor, defining a second, disconnected superconducting regime in infinite-layer nickelates.","keywords":["infinite-layer nickelates","PrNiO2","superconductivity","parent compound","phase diagram","upper critical field","hole doping","self-doping"],"falsifier":"A direct measurement of oxygen or hydrogen content on the same films (e.g., neutron reflectometry, nuclear reaction analysis, or secondary-ion mass spectrometry) that finds substantial non-stoichiometry, or a transport experiment showing that zero resistance disappears in a film independently verified to have strictly 1:1 Pr:Ni and 2:1 O composition, would falsify the intrinsic-parent claim.","tokens_in":11469,"feed_emoji":"⚡","tokens_out":3494,"duration_ms":38926,"temperature":0.7,"pith_summary":"The paper tries to establish that pristine, stoichiometric infinite-layer PrNiO2, with no divalent cation substitution, superconducts on its own, showing zero resistance and diamagnetic shielding in uncapped films. It argues that this state is not an interface effect, survives isovalent rare-earth substitution, and is destroyed by just 3% hole doping. The phase diagram therefore contains two separate superconducting regions: a narrow one near the undoped parent and the familiar dome near ~20% Sr/Ca doping, separated by a non-superconducting gap. If correct, this breaks the cuprate-like single-dome picture and requires a distinct pairing mechanism for nickelates.","feed_headline":"Undoped nickelate superconducts, splitting the phase map","feed_subtitle":"Zero resistance and diamagnetism in pristine PrNiO2 reveal a second superconducting regime, separate from the known doped dome.","key_machinery":"The load-bearing object is the doping phase diagram of infinite-layer nickelates plotted against the Ni 3dx2−y2 hole concentration measured by ARPES. The argument is carried by three experimental moves: stoichiometry optimization via Pr/Ni flux-ratio tuning, which yields low-resistivity films with zero resistance; heterostructure isolation using a non-superconducting Pr0.97Ca0.03NiO2 spacer, which excludes interface-driven superconductivity; and transport plus tunnel-diode-oscillator diamagnetism, which establish the two hallmarks of superconductivity in uncapped films.","core_discovery":"The paper claims that superconductivity near the parent limit of infinite-layer nickelates is intrinsic to undoped PrNiO2 and not the low-doping tail of the previously known hole-doped dome. Zero resistance at about 7 K and a diamagnetic response are reported in eight stoichiometric, uncapped PrNiO2 films, and the transition persists when a non-superconducting Pr0.97Ca0.03NiO2 spacer separates the film from the SrTiO3 substrate. Isovalent La substitution preserves the superconducting state, while dilute Sr or Ca substitution (1–3%) suppresses it. Combined ARPES and Hall measurements place the state at about 0.09 holes in the Ni 3dx2−y2 band, i.e., in the self-doped parent regime. The upper-c","pith_inferences":["If the parent state is real, nickelate superconductivity may be better understood as two competing instabilities—one tied to the self-doped parent and one to heavy hole doping—rather than as a single cuprate-like mechanism.","The rapid suppression by Ca/Sr without band broadening hints that the superconducting order parameter is sensitive to the filling of the electron-like β pocket; tracking β-pocket size under doping would test this.","The coherence-length and effective-layer-thickness estimates imply a condensate extending over roughly ten unit cells, which could be checked directly by scanning superconducting quantum interference device or muon spin rotation measurements.","The paper leaves open the possibility that the parent state is connected to an electron-doped superconducting regime; electron doping by gating or substitution would be a decisive test."],"forward_implications":["Infinite-layer nickelates would host two distinct superconducting states, so theories must separately explain the parent state and the ~20% doped dome.","The parent state's large upper-critical-field anisotropy (~68) suggests a more two-dimensional character than the optimally doped films, possibly pointing to a different pairing symmetry or mechanism.","Because superconductivity is killed by only 3% hole doping without added disorder, the parent state is electronically fragile and sensitive to small changes in filling.","The broad non-superconducting region between the parent state and the hole-doped dome offers a natural testbed for competing electronic orders.","The phase diagram would impose new constraints on microscopic models of nickelate superconductivity, including proposals of d+is pairing or electron-doped instabilities."],"fun_headline_variants":["Pure nickelate shows intrinsic superconductivity, a new phase","Undoped PrNiO2 superconducts: a regime separate from the doped dome","Zero resistance in pristine nickelate reveals distinct superconducting state","Parent nickelate superconducts, challenging cuprate analog view","New superconducting regime emerges at parent limit of nickelates"],"cache_read_input_tokens":2304,"weakest_assumption_plain":"The claim rests on the films being truly stoichiometric PrNiO2; no direct composition or oxygen-content measurement is shown, so if the 'pristine' films actually contain interstitial oxygen, hydrogen, or other unintended carriers, the superconductivity would not be intrinsic to the undoped parent.","fun_headline_variants_meta":{"raw":{"variants":["Pure nickelate shows intrinsic superconductivity, a new phase","Undoped PrNiO2 superconducts: a regime separate from the doped dome","Zero resistance in pristine nickelate reveals distinct superconducting state","Parent nickelate superconducts, challenging cuprate analog view","New superconducting regime emerges at parent limit of nickelates"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000856,"raw_usage":{"total_tokens":3561,"prompt_tokens":754,"completion_tokens":2807,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":498,"completion_tokens_details":{"reasoning_tokens":2722}},"tokens_in":498,"tokens_out":2807,"duration_ms":18710,"temperature":1.0,"reasoning_tokens":2722,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-01T20:14:03.898482+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A direct measurement of oxygen or hydrogen content on the same films (e.g., neutron reflectometry, nuclear reaction analysis, or secondary-ion mass spectrometry) that finds substantial non-stoichiometry, or a transport experiment showing that zero resistance disappears in a film independently verified to have strictly 1:1 Pr:Ni and 2:1 O composition, would falsify the intrinsic-parent claim.","supporting_citations":[],"review_version":1}