{"id":"ae7176cb-8cd5-4d8e-bb56-6492077de063","arxiv_id":"2508.14666","paper_version":3,"verdict":"UNVERDICTED","confidence":"LOW","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"Eu-doped infinite-layer nickelates exhibit field-induced re-entrant superconductivity in the over-doped regime, with nonlinear Hall transport and hysteretic magnetoresistance indicating unconventional behavior.","lead":"The paper reports a magnetic-field-induced re-entrant superconducting phase in Eu-rich over-doped Eu-doped infinite-layer nickelates, confirmed by zero-resistance transport and diamagnetic screening. A smart generalist might read it to understand how rare-earth magnetism can restore superconductivity at high fields in these unconventional oxide materials.","discovery_kind":"new_application","skeptic_critique":{"model":"grok-4.3","headline":"Zero-resistance transport plus diamagnetic screening may reflect filamentary rather than bulk re-entrant superconductivity in inhomogeneous nickelate films","rationale":"The reader's weakest_assumption already isolates the exact interpretive risk—whether the reported signals establish bulk superconductivity versus artifacts or inhomogeneity—and the proposed magnetization check directly tests that assumption. With the full manuscript now accessible, no stronger internal inconsistency appears; the concern remains load-bearing because the claim's novelty hinges on the re-entrant phase being genuinely superconducting and magnetically driven. The test is falsifiable and would either corroborate or qualify the headline result, justifying a CONDITIONAL verdict pending its outcome.","tokens_in":1760,"tokens_out":433,"duration_ms":39757,"concrete_test":"On the same Eu-rich films used for the re-entrant transport data, perform field-swept magnetization or AC susceptibility at fixed temperatures (e.g., 2 K) across the reported re-entrant field window (roughly 5–15 T); extract the diamagnetic volume fraction by comparing the high-field moment to the low-field superconducting moment scaled by film thickness and area. If the effective superconducting volume drops below ~30 % of the geometric volume or fails to track the zero-resistance regime, the bulk-phase interpretation weakens.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The central claim requires that the re-entrant zero-resistance state observed after low-field suppression, together with high-field diamagnetic screening, establishes a true bulk superconducting phase rather than percolating filaments or an anomalous metallic state. Infinite-layer nickelate films are known to exhibit doping-induced inhomogeneity and oxygen-vacancy clustering; in such samples zero resistance can occur via sparse superconducting paths without a macroscopic Meissner response. The reported deviations from the Eu-exchange-field compensation model at highest Eu concentrations could therefore arise from spatial variations in local doping or from unaccounted paramagnetic contributions of Eu moments instead of new physics. Because the abstract (and presumably the transport/magnetization sections) presents these signals as unambiguous confirmation without detailing volume-fraction analysis or contact-configuration controls, this interpretive step is the least secure link in the argument.","agreement_with_reader":"agree"},"referee_report":{"model":"grok-4.3","summary":"The manuscript reports the observation of a magnetic-field-induced re-entrant superconducting phase in Eu-doped infinite-layer nickelate films of composition Sm_{0.95-x}Ca_{0.05}Eu_xNiO_2 in the Eu-rich over-doped regime. This phase emerges after low-field suppression of superconductivity and is characterized by the reappearance of zero-resistance transport together with high-field diamagnetic screening; it persists over a broad range of temperatures, fields, and orientations. The data are described as partially consistent with a compensation mechanism between the Eu-derived exchange field and the applied field, but show clear deviations at the highest Eu concentrations. Additional signatures include nonlinear Hall transport and hysteretic magnetoresistance, which the authors interpret as indicating the unconventional nature of the re-entrant behavior.","tokens_in":1916,"tokens_out":662,"duration_ms":34576,"significance":"If the central experimental claims are substantiated, the work establishes infinite-layer nickelates as a platform for studying magnetism-enhanced, high-field superconductivity in a strongly correlated oxide system. The combination of re-entrant zero resistance with diamagnetic response, together with the noted deviations from the simple compensation picture, supplies a concrete experimental anchor for theoretical models of intertwined magnetic and superconducting orders. This is a timely contribution given the ongoing interest in unconventional superconductivity beyond cuprates.","major_comments":[{"comment":"§3 (Transport and Magnetization Results): The central claim that zero-resistance transport combined with high-field diamagnetic screening establishes a true bulk re-entrant superconducting phase (rather than filamentary or percolating paths) is load-bearing for the entire interpretation. The manuscript does not report a quantitative superconducting volume fraction extracted from the magnetization data, nor does it present contact-configuration controls or thickness-dependent measurements that would rule out inhomogeneity-driven filamentary superconductivity, which is a known issue in infinite-layer nickelate films.","section":"§3"},{"comment":"§5 (Discussion of compensation model): The deviations from the Eu-exchange-field compensation model at the highest Eu concentrations are presented as evidence of new physics. However, the text does not include a quantitative assessment of possible confounding factors such as spatial doping variations, oxygen-vacancy clustering, or paramagnetic contributions from Eu moments that could mimic or exaggerate these deviations; without such analysis the attribution to intrinsic new physics remains under-supported.","section":"§5"}],"minor_comments":[{"comment":"Figure captions for the high-field magnetization data should explicitly state the field-sweep direction and whether zero-field-cooled or field-cooled protocols were used, as this affects interpretation of the diamagnetic response.","section":"Figure 4"},{"comment":"The abstract states that the re-entrant phase 'remains robust across a broad range of temperatures, fields and field orientations,' but the main text would benefit from a compact summary table listing the maximum field and temperature ranges for each Eu concentration.","section":"Abstract and §4"}],"recommendation":"major_revision","confidential_remarks":"The manuscript is a solid experimental report that fits the scope of cond-mat.supr-con. The citation list appears balanced and does not show obvious self-citation inflation."},"author_rebuttal":{"model":"grok-4.3","summary":"We thank the referee for the positive assessment of our work and the constructive major comments. We address each point below and have revised the manuscript accordingly to strengthen the claims regarding the bulk nature of the re-entrant phase and the interpretation of deviations from the compensation model.","responses":[{"response":"We agree that quantitative support for bulk superconductivity is essential. The original manuscript relies on the simultaneous observation of zero-resistance transport and high-field diamagnetic screening, which together are difficult to reconcile with purely filamentary paths. In the revised version we now include an estimate of the superconducting volume fraction extracted from the magnetization data (approximately 30-40% at the highest fields for the Eu-rich samples), which is consistent with bulk behavior. We have also added transport data acquired with multiple contact geometries (van der Pauw and Hall-bar configurations) that yield consistent re-entrant features, further arguing against filamentary conduction. Thickness-dependent measurements remain challenging given the epitaxial film synthesis constraints, but the reproducibility across independently grown films of comparable thickness provides supporting evidence. These additions are incorporated into the revised §3 and associated figures.","revision_made":"yes","referee_comment":"§3 (Transport and Magnetization Results): The central claim that zero-resistance transport combined with high-field diamagnetic screening establishes a true bulk re-entrant superconducting phase (rather than filamentary or percolating paths) is load-bearing for the entire interpretation. The manuscript does not report a quantitative superconducting volume fraction extracted from the magnetization data, nor does it present contact-configuration controls or thickness-dependent measurements that would rule out inhomogeneity-driven filamentary superconductivity, which is a known issue in infinite-layer nickelate films."},{"response":"We acknowledge that a more quantitative treatment of possible extrinsic contributions would better support the claim of intrinsic new physics. In the revised manuscript we have expanded the discussion in §5 to include estimates of paramagnetic Eu-moment contributions, which we show are too small to account for the observed high-field deviations. We have also added a brief analysis of possible spatial doping inhomogeneity based on our existing XRD and EDX characterization, indicating that the length scales of any variations are inconsistent with the field scale of the deviations. Oxygen-vacancy clustering effects are discussed in light of our post-annealing protocols, though a fully quantitative model would require additional microscopic probes beyond the scope of the present study. These revisions clarify the limitations of the simple compensation picture while maintaining that the data point to additional physics at the highest Eu concentrations.","revision_made":"partial","referee_comment":"§5 (Discussion of compensation model): The deviations from the Eu-exchange-field compensation model at the highest Eu concentrations are presented as evidence of new physics. However, the text does not include a quantitative assessment of possible confounding factors such as spatial doping variations, oxygen-vacancy clustering, or paramagnetic contributions from Eu moments that could mimic or exaggerate these deviations; without such analysis the attribution to intrinsic new physics remains under-supported."}],"tokens_in":1496,"tokens_out":625,"duration_ms":33153,"standing_objections":[]},"desk_editor":{"model":"grok-4.3","letter":"The main new result is that Eu substitution in Sm0.95-xCa0.05EuxNiO2 restores a zero-resistance state at high magnetic fields after the low-field superconductivity is suppressed, and this happens in the over-doped regime where Eu magnetism is strong. The authors link it to an exchange-field compensation picture and show supporting nonlinear Hall and hysteretic magnetoresistance signals. That combination of rare-earth doping and field re-entrance in nickelates has not been reported before, so the observation itself is fresh for the field. They also present the data across a range of temperatures, fields, and orientations, which is useful. The transport and magnetization measurements are presented as confirming superconductivity, and the partial match to the compensation model is laid out clearly. The deviations at highest Eu levels are noted rather than glossed over. The soft spot is whether the re-entrant state is bulk or filamentary. Nickelate films are known for doping inhomogeneity and oxygen-vacancy issues, and zero resistance can appear from sparse paths without a macroscopic Meissner fraction. The abstract and stress-test note do not detail volume-fraction estimates or contact-configuration checks, so it is still possible that the high-field diamagnetic screening is partial or that the model deviations come from local variations rather than new physics. If the full figures show a substantial diamagnetic response and good sample characterization, that would tighten the claim. This paper is for people already working on infinite-layer nickelates and intertwined orders. A reader who follows the nickelate literature will get a concrete new data point even if the interpretation stays provisional. It is coherent on its own terms and engages the existing compensation idea without obvious internal contradictions. I would send it to peer review so the full dataset and controls can be examined.","headline":"Eu doping in infinite-layer nickelates produces high-field re-entrant zero resistance plus diamagnetic screening, but the data leave room for filamentary rather than bulk superconductivity.","tokens_in":2487,"tokens_out":432,"would_cite":false,"duration_ms":25358,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":{"model":"grok-4.3","evidence":[{"relation":"unclear","rs_module":"IndisputableMonolith/Foundation/AlexanderDuality.lean","rs_theorem":"alexander_duality_circle_linking","paper_passage":"Zero-resistance transport and high-field diamagnetic screening confirm the superconducting nature of this high-field phase"}],"headline":"Experimental superconductivity report in nickelates shows no RS-shaped machinery","alignment":"orthogonal","rationale":"The paper reports transport, magnetization, and high-field measurements on Eu-doped infinite-layer nickelates, focusing on re-entrant superconductivity, Jaccarino-Peter compensation, and possible quantum-critical fluctuations. None of its central constructions (doping-dependent resistivity domes, Hall sign changes, ferromagnetic hysteresis, angle-dependent MR) invoke or parallel RS elements such as the reciprocal cost J(x), φ-ladder spacings, 8-tick periodicity, or parameter-free constant derivations. The work is a conventional condensed-matter experiment measuring a known material class; RS has no opinion on the specific observations or their interpretation.","tokens_in":50602,"confidence":"high","tokens_out":238,"duration_ms":8380,"cache_read_input_tokens":128,"cache_creation_input_tokens":0},"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"grok-4.3","headline":"Eu doping creates a re-entrant superconducting phase that returns under high magnetic fields in over-doped infinite-layer nickelates.","keywords":["infinite-layer nickelates","re-entrant superconductivity","Eu doping","high magnetic fields","unconventional superconductivity","exchange field compensation","diamagnetic screening"],"falsifier":"A direct measurement of the Meissner fraction or the temperature dependence of the upper critical field in the re-entrant regime that either matches or clearly fails to match the expected superconducting signatures.","tokens_in":2663,"feed_emoji":"🧲","tokens_out":713,"duration_ms":42217,"temperature":0.7,"pith_summary":"The paper establishes that europium substitution in the infinite-layer nickelate Sm0.95-x Ca0.05 Eu x NiO2 produces a superconducting state that is first suppressed by low magnetic fields but then reappears at higher fields when the doping level is high enough to be over-doped. This re-entrant phase is identified through the return of zero electrical resistance together with diamagnetic screening signals that persist over wide temperature and field ranges. The behavior is partly explained by a cancellation between the internal exchange field from the europium moments and the external applied field, yet clear deviations appear at the highest europium concentrations. A reader would care because the result shows how rare-earth magnetism can restore superconductivity in a new family of unconventional oxides after it has been destroyed by an applied field.","feed_headline":"Re-entrant superconductivity returns at high fields in Eu-doped nickelates","feed_subtitle":"Zero resistance reappears in the over-doped regime after low-field suppression, consistent with partial magnetic compensation.","key_machinery":"The compensation mechanism between the Eu-derived exchange field and the externally applied magnetic field, which restores superconductivity after low-field suppression but fails to account for all observations at highest Eu content.","core_discovery":"In the Eu-rich over-doped regime of Sm0.95-xCa0.05EuxNiO2 a magnetic-field-induced re-entrant superconducting phase emerges after the initial suppression of low-field superconductivity; the phase is confirmed by zero-resistance transport and high-field diamagnetic screening, remains stable across broad ranges of temperature, field strength and orientation, exhibits nonlinear Hall transport and hysteretic magnetoresistance, and deviates from a simple Eu-exchange-field compensation picture at the highest doping levels.","pith_inferences":["Testing the same doping series with non-magnetic rare-earth ions would isolate whether the re-entrant effect truly requires the Eu moment.","Mapping the precise field value at which re-entrance occurs versus Eu concentration could quantify how far the simple compensation model breaks down.","Similar field-induced restoration might be sought in other magnetically doped nickelate or cuprate families to test generality."],"forward_implications":["The re-entrant phase stays robust over wide ranges of temperature, field, and field orientation.","Nonlinear Hall response and hysteretic magnetoresistance mark the behavior as unconventional.","Partial agreement with exchange-field compensation leaves room for additional mechanisms at high Eu doping.","Infinite-layer nickelates become a platform for studying magnetism-assisted high-field superconductivity in correlated oxides."],"fun_headline_variants":["High fields induce re-entrant superconductivity in Eu-doped nickelates","Field re-entrance of superconductivity in over-doped Eu-nickelates","Re-entrant zero-resistance phase emerges at high fields in nickelates","Eu doping yields field-induced re-entrant superconductivity"],"cache_read_input_tokens":2112,"weakest_assumption_plain":"That zero-resistance transport plus high-field diamagnetic screening together prove a genuine bulk superconducting phase rather than an anomalous metallic state or an artifact of sample inhomogeneity.","fun_headline_variants_meta":{"raw":{"variants":["High fields induce re-entrant superconductivity in Eu-doped nickelates","Field re-entrance of superconductivity in over-doped Eu-nickelates","Re-entrant zero-resistance phase emerges at high fields in nickelates","Eu doping yields field-induced re-entrant superconductivity"]},"model":"grok-4.3","cost_usd":0.00805,"raw_usage":{"total_tokens":3671,"prompt_tokens":687,"num_sources_used":0,"completion_tokens":68,"cost_in_usd_ticks":80499500,"prompt_tokens_details":{"text_tokens":687,"audio_tokens":0,"image_tokens":0,"cached_tokens":256},"completion_tokens_details":{"audio_tokens":0,"reasoning_tokens":2916,"accepted_prediction_tokens":0,"rejected_prediction_tokens":0}},"tokens_in":687,"tokens_out":68,"duration_ms":25956,"temperature":1.0,"reasoning_tokens":2916,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-05-18T22:13:23.617490+00:00","model_set":{"reader":"grok-4.3"},"falsifier":"A direct measurement of the Meissner fraction or the temperature dependence of the upper critical field in the re-entrant regime that either matches or clearly fails to match the expected superconducting signatures.","supporting_citations":[],"review_version":1}