# Nickelate superconductors: structure before comparison

Keep infinite-layer films and bilayer Ruddlesden-Popper nickelates distinct, with pressure, reduction, oxygen and strain attached to every claim.

## Scope

Nickelate superconductors include infinite-layer reduced films, bilayer Ruddlesden–Popper crystals and engineered layer sequences. The number of NiO2 layers, oxygen coordination and sample preparation distinguish these systems. An ambient-pressure epitaxial film and a compressed bulk crystal should retain separate records even when both contain lanthanum and nickel. Structural resemblance to cuprates motivates comparisons without establishing a shared pairing mechanism. [R1](#ref-source-35fd62b7cb3c490c) [R2](#ref-source-df0c15d62982f853) [R4](#ref-source-2337a5bf19bca4c4)

The 2026 La2PrNi2O7 high-field transport study concerns a bilayer Ruddlesden–Popper film. The inherited draft incorrectly placed it in the infinite-layer family. Its field-induced normal state is also distinct from the Eu-substituted infinite-layer material exhibiting re-entrant resistance suppression. Family, composition and probe must accompany these interpretations. [R6](#ref-source-1b4b1103f747fe70) [R7](#ref-source-3504ee9027165d0a)

## Mathematical assumptions

Formal charge neutrality gives nickel valence $v_{\mathrm{Ni}}=1+x+2\delta$ for an idealized $R_{1-x}\mathrm{Sr}_x\mathrm{NiO}_{2+\delta}$ with trivalent $R$, divalent Sr and divalent oxygen. For $R_3\mathrm{Ni}_2\mathrm{O}_{7-\delta}$, it gives $v_{\mathrm{Ni}}=2.5-\delta$. Sixty-six exact bookkeeping checks preserve neutrality. These averages do not measure orbital occupancy, vacancy location, ligand holes or mobile carriers. In particular, an annealing-gas dose does not specify oxygen stoichiometry. [R1](#ref-source-35fd62b7cb3c490c) [R5](#ref-source-3f4ceab12660ad62)

Even the elementary two-carrier low-field Drude expression $R_H=(p\mu_h^2-n\mu_e^2)/[e(p\mu_h+n\mu_e)^2]$, with $e>0$, prevents a unique carrier count from Hall sign alone. The ambiguity can persist when zero-field conductivity is also known. In synthetic normalized units with $e=1$, the tuples $(n,p,\mu_e,\mu_h)=(2,1,2,1)$ and $(1,2,3,1)$ both give $\sigma_0=n\mu_e+p\mu_h=5$ and $R_H=-7/25$, despite opposite majority populations. Exact inversion of the finite-field conductivity tensor checks this common low-field limit; the two finite-field curves differ. These examples assume an ordinary isotropic two-carrier normal state with $\mu_e B,\mu_h B\ll1$, excluding anomalous Hall and vortex contributions. They are local counterexamples, not fits to nickelate data. Li and Hsu discuss multiband limitations, so a negative Hall coefficient must not be silently converted to a single-band electron density. [R1](#ref-source-35fd62b7cb3c490c) [R6](#ref-source-1b4b1103f747fe70)

## Experimental criteria

For the representative Nd0.8Sr0.2NiO2 film in Li's 2019 discovery, the published text identifies a 14.9 K onset by maximum curvature, a 13.6 K midpoint and 9.1 K resistance indistinguishable from the noise floor. The final methods describe six-point electrical measurements, 9–11 nm perovskite precursor films and topotactic reduction; precursor thickness is not an independently measured reduced-film thickness. Two-coil mutual inductance supports a diamagnetic response, but the authors explicitly decline to extract a penetration depth because of finite-size, order-parameter and disorder uncertainties. The 2.2 μm value discussed nearby belongs to a cited 40 nm infinite-layer copper oxide comparison film, not a measured nickelate penetration depth. The three transition temperatures describe different criteria on the selected nickelate sample. [R1](#ref-source-35fd62b7cb3c490c)

Sun's 2023 bilayer-crystal report gives an 80 K resistance onset at 18.5 GPa in run 1 without pressure medium. Run 2 uses KBr and reaches a 78 K onset at 18.9 GPa. Figure 3 distinguishes the 10 μA run-1 excitation from 300 μA in run 2. Its magnetic response near 77 K is measured separately at 25.2 GPa. Residual resistance and specimen differences prevent combining these observations into one zero-resistance or bulk-fraction record. [R2](#ref-source-df0c15d62982f853)

## Oxygen, strain and transport

Bhatt's final strain study distinguishes nominal substrate mismatch from measured strain: the strongly compressed film is labelled approximately −1.6% measured strain, rather than the inherited draft's −1.8%. Growth method, oxygen treatment and substrate vary across comparisons. In-plane compression accompanied by out-of-plane expansion is not equivalent to hydrostatic compression. The [strain](/scwiki/strain) article retains the source-specific structural comparison and its confounding variables. [R3](#ref-source-4b5b65a5047eb1a9)

Xiang's revised author manuscript demonstrates an oxygen-removal and ozone-annealing sequence that can recover degraded bilayer films. Repeating ozone treatment alone can instead damage the superconducting response. Its proposed phase diagram uses cumulative annealing-gas volume; oxygen concentration is not precisely measured, and unknown phases complicate interpretation. Figure 2 identifies a zero-resistance point near 5.5 K for sample S1049-4, far below its onset region. The recovery experiment constrains preparation sensitivity without establishing a calibrated carrier-density axis or a universal recycling recipe. [R5](#ref-source-3f4ceab12660ad62)

Hsu's final La2PrNi2O7 study defines 41 K using 90% of a fitted normal-state resistivity. Pulsed-field measurements access a low-temperature normal state with approximately quadratic resistivity; an extrapolated zero-field normal-state curve is not directly observed below the transition. The film is about 5 nm thick, grown on SrLaAlO4 with a SrTiO3 cap and kept cold between measurements. The reported effective mass uses an empirical Kadowaki–Woods relation, not direct calorimetry. These results describe a strained bilayer specimen, not every nickelate. [R6](#ref-source-1b4b1103f747fe70)

## Recent structures and membranes

Nie's publisher abstract, published in April 2026, reports ambient-pressure onset temperatures spanning 46–50 K in engineered 1212 and 2323 layer sequences, alongside a nonsuperconducting 1313 comparison. The exact operational criterion and lower nondetection bound have not been extracted here, so this range is not assigned to a precise searchable Tc record. Associated orbital and Fermi-surface observations constrain structure–electronic-state relationships; they do not independently prove a unique pairing interaction. [R4](#ref-source-2337a5bf19bca4c4)

Lee's April 2026 membrane preprint reports 74.2 K at 91.5 GPa using 99.5% of an extrapolated normal-state resistance. Extended Data Figure 1 gives 69.1 K with an intersection construction and 75.4 K with a second-derivative construction for the illustrated transition. These differences are criterion dependence, not separate superconducting phases. Zero resistance is defined by the noise floor and occurs lower. The preprint remains explicitly labelled and is not an ambient-pressure result. [R8](#ref-source-0886448b2b71c919)

The same preprint measures six membranes and fits an onset increase near 0.65 K/GPa over its sampled range. It uses room-temperature ruby calibration below 50 GPa and diamond Raman calibration above that, with the latter measured adjacent to the specimen. Silicone-oil solidification and nonhydrostatic stress complicate broadening. Its 13 T field measurements and fitted coherence lengths should not be mistaken for direct measurements of a much larger zero-temperature critical field. Extrapolating the pressure trend beyond the measured range is not a demonstrated materials prediction. [R8](#ref-source-0886448b2b71c919)

## Limits and disputes

Yang's author manuscript identifies an approximately 54-unit-cell Eu-substituted infinite-layer SCE0.34 film whose resistance returns to zero above 6.23 T at 2 K with field along the c axis. Its separate temperature sweeps show a mutual-inductance screening response at 9 T and 12 T, absent at 3 T. This magnetic evidence supports re-entrant superconductivity beyond a resistance drop alone; 2 K is the field-sweep measurement temperature, not a new transition temperature. Magnetic compensation and triplet pairing remain proposed interpretations, and long-range magnetic order is not established. The [re-entrant superconductivity](/scwiki/field-induced-superconductivity) and [magnetic substitution](/scwiki/magnetic-substitution-and-superconductivity) articles retain the measurement windows and alternative mechanisms. None of these observations establishes a universal nickelate gap symmetry. [R7](#ref-source-3504ee9027165d0a)

Complete scientific acceptance remains open. This is an editorial review-status statement: the cited studies supply examples of differing evidence and criteria, not certification of this article. Selected primary passages, figures and local model checks have been reviewed, while full supplements, complete final-author version comparisons, independent reproduction and raw-data analysis remain incomplete. Onset, midpoint, noise-floor zero, spectroscopic gaps and normal-state measurement temperatures retain distinct meanings. Pressure and strain comparisons require matching phase and preparation rather than ordering headline temperatures. [R1](#ref-source-35fd62b7cb3c490c) [R2](#ref-source-df0c15d62982f853) [R3](#ref-source-4b5b65a5047eb1a9) [R8](#ref-source-0886448b2b71c919)

## Discovery implications

A useful comparison records layer sequence, oxygen history, nominal and measured composition, substrate, thickness, pressure calibration, probe and temperature criterion. Controlled oxygen cycles and structural contrasts are informative only with their phase and interface changes documented. A promising design hypothesis should specify which variable changes, which confounders remain and what observation would distinguish competing mechanisms. [R3](#ref-source-4b5b65a5047eb1a9) [R4](#ref-source-2337a5bf19bca4c4) [R5](#ref-source-3f4ceab12660ad62)

## Related topics

Continue with [cuprates](/scwiki/cuprates), [strain](/scwiki/strain), [two-dimensional interfaces](/scwiki/two-dimensional-interfaces), [multiband pairing](/scwiki/multiband-pairing), and [magnetic substitution](/scwiki/magnetic-substitution-and-superconductivity).

## Material cases

Values describe individual reports, not a ranking. Unknown means the checked source did not supply the field at this review scope.

| Material and sample | Reported temperature | Criterion | Probe | Pressure | State | Evidence |
|---|---|---|---|---|---|---|
| Nd0.8Sr0.2NiO2 (aliases: nickelate, nickelates); topotactically reduced epitaxial infinite-layer film | 14.9 K; Li2019 representative sample14.9K maximum-curvature onset;13.6Kmidpoint and9.1Knoise-floorzero are separate criteria. | transition; resistive-onset-maximum-curvature | Six-point resistance; capped reduced epitaxialfilm | ambient; unknown GPa | unknown | experiment; [source](#ref-source-35fd62b7cb3c490c) |
| La3Ni2O7 (aliases: nickelate, nickelates); Sun2023 run1 bilayer single crystal; no pressure-transmitting medium | 80 K; Resistance onset at 18.5 GPa; nonzero residual resistance. Separate magnetic response must not be merged into this specimen/pressure record. | transition; resistance-onset | Four-probe resistance; 10 μA; room-temperature ruby pressure calibration | high; 18.5 to 18.5 GPa | equilibrium | experiment; [source](#ref-source-df0c15d62982f853) |
| Nd0.8Sr0.2NiO2 (aliases: nickelate, nickelates); topotactically reduced epitaxial infinite-layer film | 13.6 K; Li2019 representative sample 13.6K resistive-midpoint;zero means noise floor. | transition; resistive-midpoint | Six-point resistance; capped reduced epitaxialfilm | ambient; unknown GPa | unknown | experiment; [source](#ref-source-35fd62b7cb3c490c) |
| Nd0.8Sr0.2NiO2 (aliases: nickelate, nickelates); topotactically reduced epitaxial infinite-layer film | 9.1 K; Li2019 representative sample 9.1K zero-resistance;zero means noise floor. | transition; zero-resistance | Six-point resistance; capped reduced epitaxialfilm | ambient; unknown GPa | unknown | experiment; [source](#ref-source-35fd62b7cb3c490c) |
| La2PrNi2O7 (aliases: nickelate, nickelates, LPNO, bilayer nickelate); Hsu2026 bilayerRP film onSLAO,about5nm,STOcap | 41 K; 90% of fittednormalstate,notzero;bilayerRP notinfinite-layer. | transition; resistive-90-percent-normal-fit | Resistance; source-specific criterion and methods | ambient; unknown GPa | unknown | experiment; [source](#ref-source-1b4b1103f747fe70) |
| La3Ni2O7−δ (aliases: nickelate, nickelates, oxygen recycling, S1049-4); Xiangauthorv2 Figure2a S1049-4 onSLAO | 5.5 K; Selectedauthorfigure zero5.5K;oxygen delta notprecisely measured. | transition; zero-resistance | Resistance; source-specific criterion and methods | ambient; unknown GPa | unknown | experiment; [source](#ref-source-3f4ceab12660ad62) |
| Nd0.85Sr0.15NiO2 (aliases: nickelate, nickelates, nickelate membrane, Lee membrane); Lee2026v1 freestanding membrane, Figure1f/ExtendedData1 | 74.2 K; Preprint;99.5%normalstateonset,notzero;roomTpressure andnonhydrostatic caveats. | transition; resistive-99.5-percent-normal-fit | Resistance; source-specific criterion and methods | high; 91.5 to 91.5 GPa | unknown | experiment; [source](#ref-source-0886448b2b71c919) |

## Sources

### Ref source-35fd62b7cb3c490c

[R1] Superconductivity in an infinite-layer nickelate (2019). [DOI 10.1038/s41586-019-1496-5](https://doi.org/10.1038/s41586-019-1496-5). Publication: journal-article. Check: selected-final-transport-magnetic-and-methods-check. Checked: 2026-10-20. Final published pp624–626, online Methods PDFp5; p626 Figures3–4 visually checked. Specific sample onset14.9K maximum-curvature,midpoint13.6K,noise-floorzero9.1K; six-point contacts,two-coil response,9–11nm precursor. No extracted penetration depth or complete raw/replication audit. On2026-10-20 selected text and Fig3–4 rechecked: 2.2 micrometres is the cited 40nm copper-oxide comparator, not extracted nickelate penetration depth; 9–11nm is perovskite precursor.
### Ref source-df0c15d62982f853

[R2] Signatures of superconductivity near 80 K in a nickelate under high pressure (2023). [DOI 10.1038/s41586-023-06408-7](https://doi.org/10.1038/s41586-023-06408-7). Publication: journal-article. Check: selected-published-primary-passages-check. Checked: 2026-10-20. Selected published p496 Fig3/caption and text, plus Methods PDFp7. Resistance onset, residual resistance, separate magnetic measurement, KBr and room-temperature ruby calibration retained. Raw-data/replication review remains open. On2026-10-19 finalp496Figure3 visually rechecked: run1 10microA versus run2 300microA, magnetic393Hz/50mA; upper-critical-field186T is a fit, not applied field. On2026-10-20 p496 Fig3 and text visually rechecked; run-specific pressure, excitation and separate magnetic response retained.
### Ref source-4b5b65a5047eb1a9

[R3] Structural modifications in strain-engineered bilayer nickelate thin films (2026). [DOI 10.1038/s41586-026-10446-2](https://doi.org/10.1038/s41586-026-10446-2). Publication: journal-article. Check: selected-final-journal-figures-and-methods. Checked: 2026-10-18. Online1April2026,issue7May. Selected final pp2,4,8 and Figs1/3 visually checked. Final measured labels differ from inherited draft. Growth-method/oxygen covariates and c-axis contrast retained. Complete supplement and raw-data analysis remain open.
### Ref source-2337a5bf19bca4c4

[R4] Superconductivity and electronic structures of nickelate thin film superstructures (2026). [DOI 10.1038/s41586-026-10352-7](https://doi.org/10.1038/s41586-026-10352-7). Publication: journal-article. Check: publisher-abstract-and-date-only. Checked: 2026-10-20. Published8April2026,issue16April. Publisher PDF request returned subscription HTML, preserved as HTML; abstract accessible. 1212/2323 onset46–50K,1313 nondetection without extracted lower bound; no final methods, exact onset convention or raw-data review. On2026-10-20 retained publisher abstract reread for layer-family classification; current PDF/page retrieval did not provide full methods.
### Ref source-3f4ceab12660ad62

[R5] Stabilizing and tuning superconductivity in La3Ni2O7−δ films: Oxygen recycling protocol reveals hole-doping analogue (2026). [DOI 10.1103/h9ls-y4s7](https://doi.org/10.1103/h9ls-y4s7). Publication: journal-article. Check: selected-author-oxygen-recycling-and-figures. Checked: 2026-10-19. Authorv2 revised16January2026, journal26March2026. Selectedpp1–5 andp6methodcontinuation,Figures2–3 onpp3–4 visually checked. Oxygen concentration not precisely measured; cumulative mixed-gas volume is not delta. S1049-4 Figure2a zero5.5K; threshold-based Hc2 fits not applied field. Complete final/supplement/raw comparison open.
### Ref source-1b4b1103f747fe70

[R6] Fermi-liquid transport beyond the upper critical field in superconducting La2PrNi2O7 thin films (2026). [DOI 10.1038/s41467-026-70250-4](https://doi.org/10.1038/s41467-026-70250-4). Publication: journal-article. Check: selected-final-transport-and-methods. Checked: 2026-10-20. Published10March2026, version-of-record24April2026 per publisher. Finalselectedpp2–6; p2Figure1 visually checked. BilayerRP La2PrNi2O7,not infinite-layer. Tc41K at0.9 fittednormalresistivity; field-induced and extrapolated zero-field normalstate distinguished. Methods5nmfilms,SLAO,STOcap,coldstorage,10microA. Empirical mass estimate notdirect calorimetry; supplement/raw review open. On2026-10-20 final multiband Hall passage rechecked; carrier density cannot be inferred uniquely. Local synthetic equal-RH/equal-conductivity examples are not this study’s fitted parameters.
### Ref source-3504ee9027165d0a

[R7] Field re-entrant superconductivity in Eu-doped infinite-layer nickelates (2026). [DOI 10.1038/s41586-026-10547-y](https://doi.org/10.1038/s41586-026-10547-y). Publication: journal-article. Check: selected-author-text-and-figures. Checked: 2026-10-20. Published23April2026; read authorv3 dated25April2026, selectedpp2–8, captionsp12, methodsp13–14; Fig2p19/Fig3p20 visually checked. Full final equivalence, calibration and all raw data remain open. On2026-10-20 authorv3 Fig2/caption and mechanism discussion rechecked; about54unitcells SCE0.34 zeroR above6.23T at2K; separate 3/9/12T mutual-inductance sweeps. Publisher abstract/date checked; complete final-author equivalence not established.
### Ref source-0886448b2b71c919

[R8] High-temperature superconductivity in Nd0.85Sr0.15NiO2 membranes under pressure (2026). [DOI 10.48550/arXiv.2604.09525](https://doi.org/10.48550/arXiv.2604.09525). Publication: preprint. Check: selected-preprint-results-pressure-and-onset-check. Checked: 2026-10-19. v1 submitted10April2026; no journal reference on arXiv at check. Selectedpp3–9,p15criterion,p17pressure; p4Figure1,p5Figure2,p15ExtendedData1 visually checked. 74.2K at91.5GPa uses99.5%extrapolatednormalstate,intersection69.1K notzero. RoomTpressurecalibration,nonhydrostaticcaveat,limited13Tfieldrange and six-samplefit. No raw reanalysis or final peer-reviewed version.

## Claim evidence and conditions

### scwiki-d5-claim-scope-1

Nickelate superconductors include infinite-layer reduced films, bilayer Ruddlesden–Popper crystals and engineered layer sequences. The number of NiO2 layers, oxygen coordination and sample preparation distinguish these systems. An ambient-pressure epitaxial film and a compressed bulk crystal should retain separate records even when both contain lanthanum and nickel. Structural resemblance to cuprates motivates comparisons without establishing a shared pairing mechanism.

Evidence: experiment. Sources: source-35fd62b7cb3c490c, source-df0c15d62982f853, source-2337a5bf19bca4c4.

Source relationship: context-for-editorial-analysis. Classification synthesizes Li infinite-layer films, Sun bilayer crystals and Nie publisher-abstract engineered stacks. Keeping specimen records separate is editorial analysis; no shared pairing mechanism inferred.

Conditions: Structural family, sample, oxygen/strain history, operational temperature criterion and publication version remain explicit.

Verification scope: Named selected final/author passages and figures, original abstract or exact charge/Drude model counterexamples; no complete scientific acceptance.

### scwiki-d5-claim-scope-2

The 2026 La2PrNi2O7 high-field transport study concerns a bilayer Ruddlesden–Popper film. The inherited draft incorrectly placed it in the infinite-layer family. Its field-induced normal state is also distinct from the Eu-substituted infinite-layer material exhibiting re-entrant resistance suppression. Family, composition and probe must accompany these interpretations.

Evidence: hypothesis. Sources: source-1b4b1103f747fe70, source-3504ee9027165d0a.

Conditions: Structural family, sample, oxygen/strain history, operational temperature criterion and publication version remain explicit.

Verification scope: Named selected final/author passages and figures, original abstract or exact charge/Drude model counterexamples; no complete scientific acceptance.

### scwiki-d5-claim-mathematical-assumptions-1

Formal charge neutrality gives nickel valence $v_{\mathrm{Ni}}=1+x+2\delta$ for an idealized $R_{1-x}\mathrm{Sr}_x\mathrm{NiO}_{2+\delta}$ with trivalent $R$, divalent Sr and divalent oxygen. For $R_3\mathrm{Ni}_2\mathrm{O}_{7-\delta}$, it gives $v_{\mathrm{Ni}}=2.5-\delta$. Sixty-six exact bookkeeping checks preserve neutrality. These averages do not measure orbital occupancy, vacancy location, ligand holes or mobile carriers. In particular, an annealing-gas dose does not specify oxygen stoichiometry.

Evidence: theory. Sources: source-35fd62b7cb3c490c, source-3f4ceab12660ad62.

Source relationship: context-for-local-derivation. Charge neutrality is local ionic bookkeeping under the stated formal charges. The 66 checks do not measure oxygen content or mobile-carrier density.

Conditions: Structural family, sample, oxygen/strain history, operational temperature criterion and publication version remain explicit.

Verification scope: Named selected final/author passages and figures, original abstract or exact charge/Drude model counterexamples; no complete scientific acceptance.

### scwiki-d5-claim-mathematical-assumptions-2

Even the elementary two-carrier low-field Drude expression $R_H=(p\mu_h^2-n\mu_e^2)/[e(p\mu_h+n\mu_e)^2]$, with $e>0$, prevents a unique carrier count from Hall sign alone. The ambiguity can persist when zero-field conductivity is also known. In synthetic normalized units with $e=1$, the tuples $(n,p,\mu_e,\mu_h)=(2,1,2,1)$ and $(1,2,3,1)$ both give $\sigma_0=n\mu_e+p\mu_h=5$ and $R_H=-7/25$, despite opposite majority populations. Exact inversion of the finite-field conductivity tensor checks this common low-field limit; the two finite-field curves differ. These examples assume an ordinary isotropic two-carrier normal state with $\mu_e B,\mu_h B\ll1$, excluding anomalous Hall and vortex contributions. They are local counterexamples, not fits to nickelate data. Li and Hsu discuss multiband limitations, so a negative Hall coefficient must not be silently converted to a single-band electron density.

Evidence: theory. Sources: source-35fd62b7cb3c490c, source-1b4b1103f747fe70.

Source relationship: mixed-source-and-local-derivation. Li and Hsu support multiband interpretation limits. The equal-conductivity/equal-Hall pair and finite-field tensor checks are synthetic local derivations, not reported nickelate fits.

Conditions: Ordinary isotropic two-carrier normal state; e>0, positive populations and mobilities, low-field mu B much less than 1; synthetic e=1 pair; no anomalous Hall or vortex terms, no material fit, finite-field curves distinct.

Verification scope: Named selected final/author passages and figures, original abstract or exact charge/Drude model counterexamples; no complete scientific acceptance.

### scwiki-d5-claim-experimental-criteria-1

For the representative Nd0.8Sr0.2NiO2 film in Li's 2019 discovery, the published text identifies a 14.9 K onset by maximum curvature, a 13.6 K midpoint and 9.1 K resistance indistinguishable from the noise floor. The final methods describe six-point electrical measurements, 9–11 nm perovskite precursor films and topotactic reduction; precursor thickness is not an independently measured reduced-film thickness. Two-coil mutual inductance supports a diamagnetic response, but the authors explicitly decline to extract a penetration depth because of finite-size, order-parameter and disorder uncertainties. The 2.2 μm value discussed nearby belongs to a cited 40 nm infinite-layer copper oxide comparison film, not a measured nickelate penetration depth. The three transition temperatures describe different criteria on the selected nickelate sample.

Evidence: experiment. Sources: source-35fd62b7cb3c490c.

Source relationship: direct-support. Selected final Li text, Figs 3–4 and methods support the criterion and precursor distinctions. The cited copper-oxide penetration-depth comparison is not reassigned to nickelates.

Conditions: Li final2019, selected Nd0.8Sr0.2NiO2 film Fig3b/Fig4; onset/midpoint/noise-floor zero distinct; 9–11 nm perovskite precursor; 2.2 micrometres refers to a copper-oxide comparator.

Verification scope: Named selected final/author passages and figures, original abstract or exact charge/Drude model counterexamples; no complete scientific acceptance.

### scwiki-d5-claim-experimental-criteria-2

Sun's 2023 bilayer-crystal report gives an 80 K resistance onset at 18.5 GPa in run 1 without pressure medium. Run 2 uses KBr and reaches a 78 K onset at 18.9 GPa. Figure 3 distinguishes the 10 μA run-1 excitation from 300 μA in run 2. Its magnetic response near 77 K is measured separately at 25.2 GPa. Residual resistance and specimen differences prevent combining these observations into one zero-resistance or bulk-fraction record.

Evidence: experiment. Sources: source-df0c15d62982f853.

Conditions: Structural family, sample, oxygen/strain history, operational temperature criterion and publication version remain explicit.

Verification scope: Named selected final/author passages and figures, original abstract or exact charge/Drude model counterexamples; no complete scientific acceptance.

### scwiki-d5-claim-oxygen-strain-and-transport-1

Bhatt's final strain study distinguishes nominal substrate mismatch from measured strain: the strongly compressed film is labelled approximately −1.6% measured strain, rather than the inherited draft's −1.8%. Growth method, oxygen treatment and substrate vary across comparisons. In-plane compression accompanied by out-of-plane expansion is not equivalent to hydrostatic compression. The [strain](/scwiki/strain) article retains the source-specific structural comparison and its confounding variables.

Evidence: experiment. Sources: source-4b5b65a5047eb1a9.

Conditions: Structural family, sample, oxygen/strain history, operational temperature criterion and publication version remain explicit.

Verification scope: Named selected final/author passages and figures, original abstract or exact charge/Drude model counterexamples; no complete scientific acceptance.

### scwiki-d5-claim-oxygen-strain-and-transport-2

Xiang's revised author manuscript demonstrates an oxygen-removal and ozone-annealing sequence that can recover degraded bilayer films. Repeating ozone treatment alone can instead damage the superconducting response. Its proposed phase diagram uses cumulative annealing-gas volume; oxygen concentration is not precisely measured, and unknown phases complicate interpretation. Figure 2 identifies a zero-resistance point near 5.5 K for sample S1049-4, far below its onset region. The recovery experiment constrains preparation sensitivity without establishing a calibrated carrier-density axis or a universal recycling recipe.

Evidence: experiment. Sources: source-3f4ceab12660ad62.

Conditions: Structural family, sample, oxygen/strain history, operational temperature criterion and publication version remain explicit.

Verification scope: Named selected final/author passages and figures, original abstract or exact charge/Drude model counterexamples; no complete scientific acceptance.

### scwiki-d5-claim-oxygen-strain-and-transport-3

Hsu's final La2PrNi2O7 study defines 41 K using 90% of a fitted normal-state resistivity. Pulsed-field measurements access a low-temperature normal state with approximately quadratic resistivity; an extrapolated zero-field normal-state curve is not directly observed below the transition. The film is about 5 nm thick, grown on SrLaAlO4 with a SrTiO3 cap and kept cold between measurements. The reported effective mass uses an empirical Kadowaki–Woods relation, not direct calorimetry. These results describe a strained bilayer specimen, not every nickelate.

Evidence: experiment. Sources: source-1b4b1103f747fe70.

Conditions: Structural family, sample, oxygen/strain history, operational temperature criterion and publication version remain explicit.

Verification scope: Named selected final/author passages and figures, original abstract or exact charge/Drude model counterexamples; no complete scientific acceptance.

### scwiki-d5-claim-recent-structures-and-membranes-1

Nie's publisher abstract, published in April 2026, reports ambient-pressure onset temperatures spanning 46–50 K in engineered 1212 and 2323 layer sequences, alongside a nonsuperconducting 1313 comparison. The exact operational criterion and lower nondetection bound have not been extracted here, so this range is not assigned to a precise searchable Tc record. Associated orbital and Fermi-surface observations constrain structure–electronic-state relationships; they do not independently prove a unique pairing interaction.

Evidence: experiment. Sources: source-2337a5bf19bca4c4.

Conditions: Structural family, sample, oxygen/strain history, operational temperature criterion and publication version remain explicit.

Verification scope: Named selected final/author passages and figures, original abstract or exact charge/Drude model counterexamples; no complete scientific acceptance.

### scwiki-d5-claim-recent-structures-and-membranes-2

Lee's April 2026 membrane preprint reports 74.2 K at 91.5 GPa using 99.5% of an extrapolated normal-state resistance. Extended Data Figure 1 gives 69.1 K with an intersection construction and 75.4 K with a second-derivative construction for the illustrated transition. These differences are criterion dependence, not separate superconducting phases. Zero resistance is defined by the noise floor and occurs lower. The preprint remains explicitly labelled and is not an ambient-pressure result.

Evidence: experiment. Sources: source-0886448b2b71c919.

Conditions: Structural family, sample, oxygen/strain history, operational temperature criterion and publication version remain explicit.

Verification scope: Named selected final/author passages and figures, original abstract or exact charge/Drude model counterexamples; no complete scientific acceptance.

### scwiki-d5-claim-recent-structures-and-membranes-3

The same preprint measures six membranes and fits an onset increase near 0.65 K/GPa over its sampled range. It uses room-temperature ruby calibration below 50 GPa and diamond Raman calibration above that, with the latter measured adjacent to the specimen. Silicone-oil solidification and nonhydrostatic stress complicate broadening. Its 13 T field measurements and fitted coherence lengths should not be mistaken for direct measurements of a much larger zero-temperature critical field. Extrapolating the pressure trend beyond the measured range is not a demonstrated materials prediction.

Evidence: experiment. Sources: source-0886448b2b71c919.

Conditions: Structural family, sample, oxygen/strain history, operational temperature criterion and publication version remain explicit.

Verification scope: Named selected final/author passages and figures, original abstract or exact charge/Drude model counterexamples; no complete scientific acceptance.

### scwiki-d5-claim-limits-and-disputes-1

Yang's author manuscript identifies an approximately 54-unit-cell Eu-substituted infinite-layer SCE0.34 film whose resistance returns to zero above 6.23 T at 2 K with field along the c axis. Its separate temperature sweeps show a mutual-inductance screening response at 9 T and 12 T, absent at 3 T. This magnetic evidence supports re-entrant superconductivity beyond a resistance drop alone; 2 K is the field-sweep measurement temperature, not a new transition temperature. Magnetic compensation and triplet pairing remain proposed interpretations, and long-range magnetic order is not established. The [re-entrant superconductivity](/scwiki/field-induced-superconductivity) and [magnetic substitution](/scwiki/magnetic-substitution-and-superconductivity) articles retain the measurement windows and alternative mechanisms. None of these observations establishes a universal nickelate gap symmetry.

Evidence: hypothesis. Sources: source-3504ee9027165d0a.

Source relationship: mixed-source-and-local-derivation. Selected Yang author-v3 Fig 2, caption and discussion support the observations and stated interpretation limits. Separating the 2 K measurement from Tc is editorial analysis; no independent raw-data reproduction.

Conditions: Yang authorv3 Fig2, SCE0.34 about54unitcells; H parallel c; zeroR above6.23T at2K; separate mutual-inductance temperature sweeps at3/9/12T; no universal gap-symmetry inference.

Verification scope: Named selected final/author passages and figures, original abstract or exact charge/Drude model counterexamples; no complete scientific acceptance.

### scwiki-d5-claim-limits-and-disputes-2

Complete scientific acceptance remains open. This is an editorial review-status statement: the cited studies supply examples of differing evidence and criteria, not certification of this article. Selected primary passages, figures and local model checks have been reviewed, while full supplements, complete final-author version comparisons, independent reproduction and raw-data analysis remain incomplete. Onset, midpoint, noise-floor zero, spectroscopic gaps and normal-state measurement temperatures retain distinct meanings. Pressure and strain comparisons require matching phase and preparation rather than ordering headline temperatures.

Evidence: hypothesis. Sources: source-35fd62b7cb3c490c, source-df0c15d62982f853, source-4b5b65a5047eb1a9, source-0886448b2b71c919.

Source relationship: context-for-editorial-analysis. This reports the author review coverage and unresolved work. Cited experiments illustrate criterion distinctions, and do not certify review completion or general scientific accuracy.

Conditions: Structural family, sample, oxygen/strain history, operational temperature criterion and publication version remain explicit.

Verification scope: Named selected final/author passages and figures, original abstract or exact charge/Drude model counterexamples; no complete scientific acceptance.

### scwiki-d5-claim-discovery-implications-1

A useful comparison records layer sequence, oxygen history, nominal and measured composition, substrate, thickness, pressure calibration, probe and temperature criterion. Controlled oxygen cycles and structural contrasts are informative only with their phase and interface changes documented. A promising design hypothesis should specify which variable changes, which confounders remain and what observation would distinguish competing mechanisms.

Evidence: hypothesis. Sources: source-4b5b65a5047eb1a9, source-2337a5bf19bca4c4, source-3f4ceab12660ad62.

Conditions: Structural family, sample, oxygen/strain history, operational temperature criterion and publication version remain explicit.

Verification scope: Named selected final/author passages and figures, original abstract or exact charge/Drude model counterexamples; no complete scientific acceptance.

## Revision and review

Article ID: scwiki-d5. Revision: 6f4fd4f9d32fe3e1e995. Updated: 2026-10-19T16:06:06.889215+00:00.

Review scope: Selected Li final2019 transport, Fig3–4 and methods; Hsu final2026 multiband discussion; Sun final Fig3 retained; Nie publisher abstract; Yang authorv3 Fig2/caption and mechanism limits. Exact local two-carrier nonuniqueness checked through finite-field tensor inversion. Other source-specific scopes retained; not independent review.

- Complete scientific acceptance remains open.
- Nie finalmethods and rawdata notaccessed; onsetrange remains unassigned.
- Lee membrane result is a preprint; no laterjournalversion verified.
- Xiang authorv2 notfully comparedwithfinal; annealing-gasdose isnot measuredoxygen content.
- Empirical mass and critical-field fits are not direct thermodynamic or high-field measurements.
- Equal low-field Hall slope and zero-field conductivity counterexamples are local models, not nickelate fits; finite-field curves need not coincide.

Source: [D_material_families/D5_nickelates.md](https://github.com/JackZH26/jzis-superconductivity/blob/0a7c9d6696804ec26aa12f8eed68b55c9b3c0fcf/D_material_families/D5_nickelates.md), commit 0a7c9d6696804ec26aa12f8eed68b55c9b3c0fcf, SHA-256 a2bc8ef8c14ecfec03acea7314410027b7bc91c3d3131af4dc3e933625f81a92.