{"schemaVersion":"1.0","revision":"fa961ab24277a91737c3","article":{"id":"scwiki-d9","topicId":"scwiki-topic-d9","code":"D9","slug":"fulleride-superconductors","title":"Fulleride superconductors: Jahn–Teller coupling, Mott physics and driven states","summary":"Compare alkali-doped C60 compounds through pressure, molecular interactions and sample-specific transition criteria, with explicit boundaries for driven and retracted claims.","aliases":["fullerides","fullerenes","C60","K3C60","Rb3C60","Cs3C60","Jahn–Teller","inverted Hund exchange","current-driven intercalation"],"evidenceTypes":["theory","experiment"],"relatedCodes":["B1","B2","A1","B14","C1"],"editorialStatus":"scoped-check","contentState":"pilot","modifiedAt":"2026-10-20","review":{"checkedAt":"2026-10-20","scope":"Selected fcc Cs3C60 pressure/magnetometry, fulleride model equations, 2026 intercalation transport criteria, prior scoped driven-state readings and complete indexed retraction notice. Publisher notice identifying the 24 February 2016 Mitrano caption correction checked separately on 19 October 2026. Follow-up ideal filling versus actual multiphase sample and selected final Budden Fig.4/text.","limitations":["Full scientific acceptance, complete final-version comparisons and raw-data reproduction remain open.","1991 discoveries remain abstract-level; 2008 A15 methods have not been reviewed.","The 2026 supplement and complete transient-state supplement and raw data remain outside this check.","No computed DMFT phase diagram, microscopic-mechanism uniqueness or device qualification is claimed."]},"provenance":{"repository":"JackZH26/jzis-superconductivity","commit":"0a7c9d6696804ec26aa12f8eed68b55c9b3c0fcf","path":"D_material_families/D9_fullerenes.md","sha256":"7fb6155c2847a4c14bfe3ba43e213f2ae8f83dfbe12019478fe94ca8d29cf392","sourceId":"file-2d8c8617328230a6"},"sourceMap":[{"startLine":1,"endLine":71,"targetSections":["scope","mathematical-assumptions","experimental-criteria","limits-and-disputes","discovery-implications","related-topics"],"decision":"edited-with-scoped-evidence","note":"Pinned source preserved; original retraction companion and2026 transport criteria added."}],"references":[{"id":"source-51b1a52d16139e58","doi":"10.1038/350600a0","title":"Superconductivity at 18 K in potassium-doped C60","year":1991,"url":"https://doi.org/10.1038/350600a0","publicationStatus":"journal-article","verification":{"scope":"original-abstract-check","checkedAt":"2026-10-18","evidenceUrl":"https://research.rug.nl/en/publications/superconductivity-at-18-k-in-potassium-doped-c60/","note":"Original abstract distinguishes film resistive onset16K/essentially zero5K from bulk magnetic/microwave18K. Full PDF returned403; full experimental methods not reviewed."}},{"id":"source-0fb5ae1290bd2998","doi":"10.1103/PhysRevLett.66.2830","title":"Superconductivity at 28 K in RbxC60","year":1991,"url":"https://doi.org/10.1103/PhysRevLett.66.2830","publicationStatus":"journal-article","verification":{"scope":"publisher-abstract-check","checkedAt":"2026-10-18","evidenceUrl":"https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.66.2830","note":"Published27May1991. Original abstract checked for bulk Meissner/microwave maximum28K. Full methods not reviewed; title stoichiometry remains RbxC60."}},{"id":"source-634d02f3c2bfde0d","doi":"10.1038/nmat2179","title":"Bulk superconductivity at 38 K in a molecular system","year":2008,"url":"https://doi.org/10.1038/nmat2179","publicationStatus":"journal-article","verification":{"scope":"publisher-metadata-and-later-primary-comparison","checkedAt":"2026-10-18","evidenceUrl":"https://www.nature.com/articles/nmat2179","note":"Online20April2008. Metadata checked and A15 maximum38K cross-checked against Ganin2010 original comparison. Direct PDF response was not a PDF; full original methods not reviewed."}},{"id":"source-5e6d3e7ed715ad6a","doi":"10.1038/nature09120","title":"Polymorphism control of superconductivity and magnetism in Cs3C60 close to the Mott transition","year":2010,"url":"https://doi.org/10.1038/nature09120","publicationStatus":"journal-article","verification":{"scope":"selected-published-pressure-magnetism-methods","checkedAt":"2026-10-20","evidenceUrl":"https://cienciaescolar.wordpress.com/wp-content/uploads/2010/07/nature09120.pdf","note":"Original Nature466,221–225, issue8July2010, hosted as an unchanged paper PDF. Selected pp221–222, Fig3 caption p224 and online magnetic Methods read; p222 visually inspected. Multiphase sample, pressure calibration and shielding criteria retained. Complete supplement and raw data not reanalyzed. Follow-up selected published p.221: refined Cs2.901(6)C60, about86%fcc fraction, minority phases and ambient-pressure magnetic insulating behavior; not a new whole-paper review."}},{"id":"source-e2b9d469a7c556df","doi":"10.1103/RevModPhys.81.943","title":"Colloquium: Modeling the unconventional superconducting properties of expanded A3C60 fullerides","year":2009,"url":"https://doi.org/10.1103/RevModPhys.81.943","publicationStatus":"journal-article","verification":{"scope":"selected-author-model-equations-check","checkedAt":"2026-10-20","evidenceUrl":"https://arxiv.org/pdf/0809.0910v1","note":"Authorv1 submitted4September2008; journal19June2009. Selected p5 Eq1–3, p8 model discussion and p9 heuristic Cooper amplitude read; p5 visually inspected. Independent n=3 multiplets and illustrative amplitude/unit checks, not a DMFT reproduction. Final-version comparison and complete review remain open. Follow-up author-v1 p.2 introduction: three donated electrons half-fill the molecular t1u manifold; this count alone does not establish the electronic phase."}},{"id":"source-6ee3670220e24ff1","doi":"10.1038/nature16522","title":"Possible light-induced superconductivity in K3C60 at high temperature","year":2016,"url":"https://doi.org/10.1038/nature16522","publicationStatus":"journal-article","verification":{"scope":"earlier-author-manuscript-scoped-check","checkedAt":"2026-10-19","evidenceUrl":"https://arxiv.org/pdf/1505.04529v1","note":"Reused B7/A1 scoped primary reading, with the same version and methods limitations. Inherited A1 selected pp.1–2,4–6 check: finite-window transient optical response and high-mobility alternative. The publisher’s 24 February 2016 caption-correction notice is identified; no full final-version equivalence is established."},"updates":[{"kind":"correction","date":"2016-02-24","description":"The publisher restored a truncated final sentence in the Figure 4 caption of the advance-online PDF.","evidenceUrl":"https://www.nature.com/articles/nature16522#change-history","checkedAt":"2026-10-19","scope":"Publisher change-history notice and publisher-deposited Crossref assertion agree. Old and corrected PDFs were not compared in full."}]},{"id":"source-07be806c0002c690","doi":"10.1038/s41567-020-01148-1","title":"Evidence for metastable photo-induced superconductivity in K3C60","year":2021,"url":"https://doi.org/10.1038/s41567-020-01148-1","publicationStatus":"journal-article","verification":{"scope":"selected-final-figure-and-transport-calibration","checkedAt":"2026-10-20","evidenceUrl":"https://pure.mpg.de/rest/items/item_3196913_5/component/file_3319164/content","note":"Cached final published paper p.615 Fig.4/caption and text read; figure pixels visually inspected.200ps optical and75ps transport pumps at100K,approximately25mJ/cm2; optical zero-frequency extrapolation versus transient two-terminal contact-calibrated resistance and1ns voltage probe. Supersedes earlier-manuscript-only scope for these passages. Web refetch returned403; cached final artifact retained. Complete supplement, raw-data refit and full author/final version comparison remain open."}},{"id":"source-64cd48d99353501a","doi":"10.1021/acsnano.6c02466","title":"On-Chip Tuning of Superconductivity in Fullerides via Current-Driven Rb+ Intercalation","year":2026,"url":"https://doi.org/10.1021/acsnano.6c02466","publicationStatus":"journal-article","verification":{"scope":"selected-published-transport-and-composition-methods","checkedAt":"2026-10-18","evidenceUrl":"https://research-explorer.ista.ac.at/download/22145/22150/2026_ACSNano_Shchukin.pdf","note":"Publishedonline9June2026, not repository upload29June; issue23June. Selected pp17360–17363 and electrical transport/EPC passages pp17367–17368 read. Fig2f p17362 visually inspected for separate onset and derivative-threshold temperatures. Supplement and original datasets not reanalyzed."}},{"id":"source-091fb85b144daad9","doi":"10.1038/35046008","title":"RETRACTED ARTICLE: Superconductivity at 52 K in hole-doped C60","year":2000,"url":"https://doi.org/10.1038/35046008","publicationStatus":"journal-article","verification":{"scope":"retracted-article-identity-check","checkedAt":"2026-10-18","evidenceUrl":"https://www.nature.com/articles/35046008","note":"Original30November2000 identity and retraction link checked; withdrawn52K claim is not an experimental benchmark."},"retraction":{"noticeDoi":"10.1038/nature01466","retractedAt":"2003-03-06","evidenceUrl":"https://doi.org/10.1038/nature01466"}},{"id":"source-8822fee6435cf8cc","doi":"10.1038/nature01466","title":"Retraction Note to: Superconductivity at 52 K in hole-doped C60","year":2003,"url":"https://doi.org/10.1038/nature01466","publicationStatus":"journal-article","verification":{"scope":"publisher-indexed-complete-notice-text","checkedAt":"2026-10-18","evidenceUrl":"https://www.nature.com/articles/nature01466","note":"Published6March2003. Complete indexed notice text read and original DOI link verified; concerns concern device-measurement data after independent investigation. Direct publisher HTML identity redirect unavailable."}}],"claims":[{"id":"scwiki-d9-claim-scope-1","sectionId":"scope","statement":"Alkali-doped fullerides combine molecular vibrations, narrow electronic bands and strong local interactions. Ideal A₃C₆₀ has three donated electrons in a molecular t₁ᵤ manifold with six spin-orbital states: half-filling describes electron counting, not a guarantee of metallic transport or superconductivity. The same nominal Cs₃C₆₀ composition supports fcc and A15 packings with different magnetic and pressure-dependent superconducting behavior. Specify composition, structure, preparation and measurement conditions before comparing temperatures. Pressure-induced equilibrium superconductivity and optically driven responses are separate evidence classes.\n\nNominal composition is not a sample assay. Ganin's fcc-rich powder had refined composition Cs₂.₉₀₁₍₆₎C₆₀ and an fcc fraction of about 86%, with minority phases. Its ambient-pressure magnetic insulating behavior illustrates why three donated electrons alone cannot define the phase. These preparation and phase-fraction qualifications accompany the idealized A₃C₆₀ description.","evidenceType":"theory","sourceIds":["source-e2b9d469a7c556df","source-5e6d3e7ed715ad6a","source-07be806c0002c690"],"conditions":"Ideal three-electron t1u manifold; actual fcc-rich Cs3C60 powder is multiphase, refined Cs2.901(6)C60. Pressure, polymorph, probe and optical excitation must remain attached.","verificationScope":"Selected Capone author-v1 introduction, Ganin published p.221 and Budden final p.615/Fig.4; not a full review or raw-data reproduction.","sourceRelationship":"mixed-source-and-local-derivation","derivationNote":"Capone supplies the ideal molecular electron count; Ganin supplies the polymorph, refined composition and phase-fraction evidence; Budden supplies the driven experiment. Separating nominal filling, measured composition and equilibrium/driven evidence is editorial synthesis, not a new phase calculation."},{"id":"scwiki-d9-claim-scope-2","sectionId":"scope","statement":"The 1991 potassium discovery already illustrates why one temperature is insufficient: the abstract reports a thin-film resistive onset near 16 K and essentially vanishing resistance by 5 K, while bulk magnetic and microwave measurements indicate an 18 K transition. The subsequent rubidium report gives a maximum of 28 K from bulk magnetic and microwave evidence. These abstract-level checks establish historical observations; they do not constitute a complete reassessment of the original specimens.","evidenceType":"experiment","sourceIds":["source-51b1a52d16139e58","source-0fb5ae1290bd2998"],"conditions":"Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.","verificationScope":"Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open."},{"id":"scwiki-d9-claim-mathematical-assumptions-1","sectionId":"mathematical-assumptions","statement":"One influential model represents each molecule by three effective p-like orbitals with local terms $H_U=U(n-3)^2/2$ and $H_J=J[2\\mathbf S^2+\\mathbf L^2/2]+5J(n-3)^2/6$. Angular momenta are dimensionless. In this convention ordinary Hund exchange has $J=-J_H<0$; integrating out Jahn–Teller vibrations can instead give $J=-J_H+J_{JT}>0$. This static reduction requires the coherent electronic scale $ZW$ to lie below the relevant phonon energy. It should not be applied across the whole bandwidth range without checking retardation.","evidenceType":"theory","sourceIds":["source-e2b9d469a7c556df"],"conditions":"Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.","verificationScope":"Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open."},{"id":"scwiki-d9-claim-mathematical-assumptions-2","sectionId":"mathematical-assumptions","statement":"At exactly three electrons, the model multiplets $^4S$, $^2D$ and $^2P$ have energies $15J/2$, $9J/2$ and $5J/2$, with respective degeneracies 4, 10 and 6. They account for $\\binom{6}{3}=20$ local states. Positive effective $J$ favors the low-spin $^2P$ multiplet; negative $J$ favors $^4S$. This is an algebraic check of the effective local Hamiltonian, not a measured molecular spectrum or proof of superconducting order.","evidenceType":"theory","sourceIds":["source-e2b9d469a7c556df"],"conditions":"Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.","verificationScope":"Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open."},{"id":"scwiki-d9-claim-mathematical-assumptions-3","sectionId":"mathematical-assumptions","statement":"The heuristic Cooper-channel amplitude $A^*\\simeq ZU-10J/3$ illustrates how correlations can reduce repulsion relative to an inverted exchange. For illustrative fixed ratios $U/W=0.5$ and $J/W=0.05$, its sign changes at $Z=1/3$. Simultaneously the coherent bandwidth is $ZW$: decreasing $Z$ does not supply an unlimited transition-temperature gain. The published argument explicitly allows deviations near the Mott boundary; its underlying DMFT model uses an infinite-coordination Bethe lattice. No self-consistent DMFT calculation or measured transition follows from this toy sweep.","evidenceType":"theory","sourceIds":["source-e2b9d469a7c556df"],"conditions":"Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.","verificationScope":"Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open."},{"id":"scwiki-d9-claim-experimental-criteria-1","sectionId":"experimental-criteria","statement":"For fcc Cs₃C₆₀, Ganin and colleagues report a pressure-dependent magnetic onset: 25.6 K at 1.3 kbar has only about 0.1% shielding, whereas 29.7 K at 2.2 kbar has about 12%. The maximum is approximately 35 K near 7 kbar, equivalent to 0.7 GPa. Measurements use 20 Oe, zero-field-cooled/field-cooled protocols and a tin pressure reference. A15 Cs₃C₆₀ reaches a separately reported maximum near 38 K; its value must not be assigned to the fcc sample.","evidenceType":"experiment","sourceIds":["source-634d02f3c2bfde0d","source-5e6d3e7ed715ad6a"],"conditions":"Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.","verificationScope":"Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open."},{"id":"scwiki-d9-claim-experimental-criteria-2","sectionId":"experimental-criteria","statement":"The fcc study also separates magnetic ordering near 2.2 K from the A15 ordering scale near 46 K. Neither is a superconducting transition. Multiphase powders and small shielding fractions require particular care when locating the first superconducting signal. The magnetometry pressure range ends near 10.6 kbar; the separate diffraction measurements extend to much higher pressures. Combining those ranges would falsely imply that superconductivity was measured throughout the structural experiment.","evidenceType":"experiment","sourceIds":["source-5e6d3e7ed715ad6a"],"conditions":"Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.","verificationScope":"Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open."},{"id":"scwiki-d9-claim-experimental-criteria-3","sectionId":"experimental-criteria","statement":"Published online on 9 June 2026, Shchukin and colleagues tune Rb uptake in nanostructured C₆₀ films. Figure 2f labels Rb₂.₇₁C₆₀ with $T_{\\mathrm{onset}}=22.4$ K and $T_{\\mathrm{zero}}=7.0$ K, and Rb₂.₉₈C₆₀ with 26.4 K and 14.5 K. The former criterion is a local resistivity maximum; the latter uses $d\\rho/dT<5\\times10^{-4}$ mΩ cm K⁻¹ in the plotted low-temperature window. It is a stated operational criterion, not an instrument-independent definition of exact zero resistance.","evidenceType":"experiment","sourceIds":["source-64cd48d99353501a"],"conditions":"Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.","verificationScope":"Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open."},{"id":"scwiki-d9-claim-experimental-criteria-4","sectionId":"experimental-criteria","statement":"That experiment uses Raman analysis with relative scattering cross sections to estimate composition, and van der Pauw transport. The 10 μA intercalation current differs from the 1 μA resistance-probe current. Stoichiometry, grain connectivity, thickness and transition criterion must accompany any comparison with bulk rubidium fullerides. The supplement and underlying transport datasets have not been independently reanalyzed here.","evidenceType":"experiment","sourceIds":["source-64cd48d99353501a"],"conditions":"Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.","verificationScope":"Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open."},{"id":"scwiki-d9-claim-limits-and-disputes-1","sectionId":"limits-and-disputes","statement":"Mitrano's optical study and Budden's longer-lived driven response concern pumped K₃C₆₀. A finite-frequency inductive response and suppressed transient resistance constrain the nonequilibrium state, but do not by themselves establish an equilibrium thermodynamic transition. Budden's final Figure 4 separates two measurements at a 100 K base temperature and approximately 25 mJ cm⁻² pump fluence:\n\n| Measurement | What the reported value means |\n|---|---|\n| Optical, Fig. 4a; 200 ps pump | Zero-frequency resistivity extrapolated from a Drude–Lorentz fit to transient optical conductivity; error bars reflect the fit confidence interval. |\n| Electrical, Fig. 4b; 75 ps pump | Transient two-terminal resistance after contact correction from a separate static four-terminal measurement; the shaded band estimates calibration error. |\n\nThe electrical readout uses a 1 ns voltage probe pulse. The corrected resistance is compatible with zero within the stated calibration uncertainty, and recovers on a tens-of-nanoseconds timescale. This supports the authors' assignment of a metastable superconducting state; it does not turn the 100 K measurement condition into an equilibrium Tc. Neither the pump duration nor the probe duration is the state lifetime. Both records retain `transient-response` temperatures with no equilibrium Tc. Complete supplement review, raw-data refitting and comparison of alternative conductivity models remain open.","evidenceType":"experiment","sourceIds":["source-6ee3670220e24ff1","source-07be806c0002c690"],"conditions":"Budden final Fig.4,100K base,approximately25mJ/cm2,200ps optical/75ps transport pumps; electrical1ns voltage probe; optical extrapolation and contact-corrected transient transport are distinct.","verificationScope":"Selected final published Fig.4/caption and p.615 text with figure pixels inspected; complete supplement and raw-data fits not checked.","sourceRelationship":"mixed-source-and-local-derivation","derivationNote":"Budden final Fig.4/caption and text supply distinct fit/calibration errors, 200ps and75ps pumps, 1ns voltage probe,100K base and transient recovery. Exclusion from equilibrium Tc rankings is an editorial classification; it does not claim an independent adjudication of the driven-state mechanism."},{"id":"scwiki-d9-claim-limits-and-disputes-2","sectionId":"limits-and-disputes","statement":"The historical hole-doped C₆₀ claim at 52 K was retracted on 6 March 2003. The original paper and its notice are retained together for traceability; the withdrawn value is excluded from experimental transition records. The notice identifies concerns about device-measurement data following an independent investigation. A citation in an older, otherwise valid paper does not restore the withdrawn claim.","evidenceType":"experiment","sourceIds":["source-091fb85b144daad9","source-8822fee6435cf8cc"],"conditions":"Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.","verificationScope":"Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open."},{"id":"scwiki-d9-claim-discovery-implications-1","sectionId":"discovery-implications","statement":"Fullerides motivate simultaneous control of bandwidth, local vibronic interactions, molecular valence and disorder. A superconducting dome near a Mott state is compatible with cooperation between phonons and correlations; it does not uniquely determine the pairing kernel. Neither a fully open gap nor proximity to a magnetic insulator proves that one interaction acts alone. Report model assumptions beside the experimental evidence used to constrain them.","evidenceType":"experiment","sourceIds":["source-5e6d3e7ed715ad6a","source-e2b9d469a7c556df"],"conditions":"Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.","verificationScope":"Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open."},{"id":"scwiki-d9-claim-discovery-implications-2","sectionId":"discovery-implications","statement":"Current-driven intercalation offers a method for tuning samples rather than a new bulk temperature record. Reproducible optimization needs composition maps, measurement-current controls and comparable transition definitions. Keep pressure polymorphs and optically driven states separate when selecting targets: their conditions cannot be collapsed into a single family-wide Tc ranking.","evidenceType":"experiment","sourceIds":["source-64cd48d99353501a","source-5e6d3e7ed715ad6a","source-07be806c0002c690"],"conditions":"Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.","verificationScope":"Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open."}],"corrections":[{"id":"scwiki-d9-correction-1","description":"Attached the original2003 retraction notice to the withdrawn52K claim; it supplies no accepted experimental transition record.","sourceId":"source-8822fee6435cf8cc","scope":"Public article and exported metadata; pinned source unchanged."},{"id":"scwiki-d9-correction-mitrano-caption-notice","description":"Identified the previously unspecified Mitrano update as the publisher’s 24 February 2016 correction of a truncated Figure 4 caption sentence in the advance-online PDF.","sourceId":"source-6ee3670220e24ff1","scope":"Correction-notice identity only; earlier manuscript limits, full version comparison and raw-data limitations remain."},{"id":"scwiki-d9-correction-filling-and-final-pump-probes","description":"Distinguish ideal half-filling from refined composition and phase fraction; replace earlier-manuscript-only Budden scope with selected final Fig.4, separate optical extrapolation from contact-calibrated transport, and retain100K as transient base temperature.","scope":"D9 body and machine-readable claims/material records; no new equilibrium transition and no change to the fixed source repository."}],"equationChecks":[{"targetSectionId":"mathematical-assumptions","tex":"H_J=J[2S(S+1)+L(L+1)/2]+5J(n-3)^2/6","check":"n=3 multiplet energies and20-state dimension; positive/negative J ordering checked."},{"targetSectionId":"mathematical-assumptions","tex":"A^*\\simeq ZU-10J/3","check":"Five illustrative Z values at fixed U/W=.5,J/W=.05; no self-consistent Tc calculation."}],"materialCases":[{"id":"scwiki-d9-material-1","formula":"K-doped C60","sample":"Hebard bulk specimen","recordType":"experiment","reportedTemperatureK":18,"tcK":18,"temperatureKind":"transition","temperatureNote":"Original abstract only; film 16 K onset / 5 K essentially zero are different measurements.","criterion":"magnetic-and-microwave-onset","pressureRegime":"ambient","pressureGPa":null,"equilibrium":"equilibrium","probe":"Meissner and microwave response","sourceId":"source-51b1a52d16139e58","aliases":["fulleride","fullerides"]},{"id":"scwiki-d9-material-2","formula":"RbxC60","sample":"Rosseinsky bulk discovery material","recordType":"experiment","reportedTemperatureK":28,"tcK":28,"temperatureKind":"transition","temperatureNote":"Reported maximum; full original methods not reviewed.","criterion":"magnetic-and-microwave-onset","pressureRegime":"ambient","pressureGPa":null,"equilibrium":"equilibrium","probe":"Meissner and microwave response","sourceId":"source-0fb5ae1290bd2998","aliases":["fulleride","fullerides"]},{"id":"scwiki-d9-material-3","formula":"Cs3C60","sample":"fcc polymorph, trace shielding","recordType":"experiment","reportedTemperatureK":25.6,"tcK":25.6,"temperatureKind":"transition","temperatureNote":"About 0.1% shielding; do not infer bulk fraction from this onset.","criterion":"magnetization-onset-trace-shielding","pressureRegime":"high","pressureGPa":{"min":0.13,"max":0.13},"equilibrium":"equilibrium","probe":"20 Oe ZFC/FC magnetometry","sourceId":"source-5e6d3e7ed715ad6a","aliases":["fulleride","fullerides"]},{"id":"scwiki-d9-material-4","formula":"Cs3C60","sample":"fcc polymorph, about 12% shielding","recordType":"experiment","reportedTemperatureK":29.7,"tcK":29.7,"temperatureKind":"transition","temperatureNote":"Pressure-specific magnetic onset in a multiphase powder.","criterion":"magnetization-onset","pressureRegime":"high","pressureGPa":{"min":0.22,"max":0.22},"equilibrium":"equilibrium","probe":"20 Oe ZFC/FC magnetometry","sourceId":"source-5e6d3e7ed715ad6a","aliases":["fulleride","fullerides"]},{"id":"scwiki-d9-material-5","formula":"Cs3C60","sample":"fcc polymorph dome maximum","recordType":"experiment","reportedTemperatureK":35,"tcK":35,"temperatureKind":"transition","temperatureNote":"Approximate maximum at approximately 7 kbar; not A15 maximum 38 K.","criterion":"magnetization-onset","pressureRegime":"high","pressureGPa":{"min":0.7,"max":0.7},"equilibrium":"equilibrium","probe":"20 Oe ZFC/FC magnetometry","sourceId":"source-5e6d3e7ed715ad6a","aliases":["fulleride","fullerides"]},{"id":"scwiki-d9-material-6","formula":"Cs3C60","sample":"fcc ambient-pressure magnetic ordering","recordType":"experiment","reportedTemperatureK":2.2,"tcK":null,"temperatureKind":"measurement","temperatureNote":"Magnetic ordering, not a superconducting Tc.","criterion":"magnetic-ordering-temperature","pressureRegime":"ambient","pressureGPa":null,"equilibrium":"equilibrium","probe":"Muon spin rotation and magnetism","sourceId":"source-5e6d3e7ed715ad6a","aliases":["fulleride","fullerides"]},{"id":"scwiki-d9-material-7","formula":"Rb2.98C60","sample":"Shchukin nanostructured film, Fig2f onset","recordType":"experiment","reportedTemperatureK":26.4,"tcK":26.4,"temperatureKind":"transition","temperatureNote":"Same film as 14.5 K derivative-threshold record; two criteria, not two independent specimens.","criterion":"local-resistivity-maximum","pressureRegime":"ambient","pressureGPa":null,"equilibrium":"equilibrium","probe":"Van der Pauw transport, 1 μA","sourceId":"source-64cd48d99353501a","aliases":["fulleride","fullerides"]},{"id":"scwiki-d9-material-8","formula":"Rb2.98C60","sample":"Shchukin nanostructured film, Fig2f low-temperature threshold","recordType":"experiment","reportedTemperatureK":14.5,"tcK":14.5,"temperatureKind":"transition","temperatureNote":"Tzero defined by dρ/dT<5e-4 mΩcm/K in plotted window; not instrument-independent exact zero.","criterion":"resistivity-derivative-threshold","pressureRegime":"ambient","pressureGPa":null,"equilibrium":"equilibrium","probe":"Van der Pauw transport, 1 μA","sourceId":"source-64cd48d99353501a","aliases":["fulleride","fullerides"]},{"id":"scwiki-d9-material-9","formula":"Rb2.71C60","sample":"Shchukin nanostructured film, Fig2f low-temperature threshold","recordType":"experiment","reportedTemperatureK":7,"tcK":7,"temperatureKind":"transition","temperatureNote":"Same operational derivative threshold as 14.5 K optimally intercalated film.","criterion":"resistivity-derivative-threshold","pressureRegime":"ambient","pressureGPa":null,"equilibrium":"equilibrium","probe":"Van der Pauw transport, 1 μA","sourceId":"source-64cd48d99353501a","aliases":["fulleride","fullerides"]},{"id":"scwiki-d9-material-10","formula":"K3C60","sample":"Budden final Fig.4b optically driven K3C60 pellet","recordType":"experiment","reportedTemperatureK":100,"tcK":null,"temperatureKind":"transient-response","temperatureNote":"100K base; approximately25mJ/cm2 fluence and75ps pump. Contact-corrected resistance compatible with zero within calibration uncertainty. Transient recovery is not an equilibrium transition; pump/probe duration is not lifetime.","criterion":"driven-resistance-suppression","pressureRegime":"ambient","pressureGPa":null,"equilibrium":"transient","probe":"Transient two-terminal transport;1ns voltage probe; static four-terminal contact calibration","sourceId":"source-07be806c0002c690","aliases":["fulleride","fullerides"]},{"id":"scwiki-d9-material-11","formula":"K3C60","sample":"Budden final Fig.4a optically driven K3C60 optical measurement","recordType":"experiment","reportedTemperatureK":100,"tcK":null,"temperatureKind":"transient-response","temperatureNote":"100K base; approximately25mJ/cm2 fluence and200ps pump. Error bars are fit confidence intervals. Extrapolated transient resistivity is not a direct equilibrium DC transport measurement or equilibrium Tc.","criterion":"driven-optical-zero-frequency-extrapolation","pressureRegime":"ambient","pressureGPa":null,"equilibrium":"transient","probe":"Drude-Lorentz fit to transient optical conductivity, extrapolated to zero frequency","sourceId":"source-07be806c0002c690","aliases":["fulleride","fullerides"]}],"body":"## Scope\n\nAlkali-doped fullerides combine molecular vibrations, narrow electronic bands and strong local interactions. Ideal A₃C₆₀ has three donated electrons in a molecular t₁ᵤ manifold with six spin-orbital states: half-filling describes electron counting, not a guarantee of metallic transport or superconductivity. The same nominal Cs₃C₆₀ composition supports fcc and A15 packings with different magnetic and pressure-dependent superconducting behavior. Specify composition, structure, preparation and measurement conditions before comparing temperatures. Pressure-induced equilibrium superconductivity and optically driven responses are separate evidence classes. [R5](#ref-source-e2b9d469a7c556df) [R4](#ref-source-5e6d3e7ed715ad6a) [R7](#ref-source-07be806c0002c690)\n\nNominal composition is not a sample assay. Ganin's fcc-rich powder had refined composition Cs₂.₉₀₁₍₆₎C₆₀ and an fcc fraction of about 86%, with minority phases. Its ambient-pressure magnetic insulating behavior illustrates why three donated electrons alone cannot define the phase. These preparation and phase-fraction qualifications accompany the idealized A₃C₆₀ description. [R4](#ref-source-5e6d3e7ed715ad6a)\n\nThe 1991 potassium discovery already illustrates why one temperature is insufficient: the abstract reports a thin-film resistive onset near 16 K and essentially vanishing resistance by 5 K, while bulk magnetic and microwave measurements indicate an 18 K transition. The subsequent rubidium report gives a maximum of 28 K from bulk magnetic and microwave evidence. These abstract-level checks establish historical observations; they do not constitute a complete reassessment of the original specimens. [R1](#ref-source-51b1a52d16139e58) [R2](#ref-source-0fb5ae1290bd2998)\n\n## Mathematical assumptions\n\nOne influential model represents each molecule by three effective p-like orbitals with local terms $H_U=U(n-3)^2/2$ and $H_J=J[2\\mathbf S^2+\\mathbf L^2/2]+5J(n-3)^2/6$. Angular momenta are dimensionless. In this convention ordinary Hund exchange has $J=-J_H<0$; integrating out Jahn–Teller vibrations can instead give $J=-J_H+J_{JT}>0$. This static reduction requires the coherent electronic scale $ZW$ to lie below the relevant phonon energy. It should not be applied across the whole bandwidth range without checking retardation. [R5](#ref-source-e2b9d469a7c556df)\n\nAt exactly three electrons, the model multiplets $^4S$, $^2D$ and $^2P$ have energies $15J/2$, $9J/2$ and $5J/2$, with respective degeneracies 4, 10 and 6. They account for $\\binom{6}{3}=20$ local states. Positive effective $J$ favors the low-spin $^2P$ multiplet; negative $J$ favors $^4S$. This is an algebraic check of the effective local Hamiltonian, not a measured molecular spectrum or proof of superconducting order. [R5](#ref-source-e2b9d469a7c556df)\n\nThe heuristic Cooper-channel amplitude $A^*\\simeq ZU-10J/3$ illustrates how correlations can reduce repulsion relative to an inverted exchange. For illustrative fixed ratios $U/W=0.5$ and $J/W=0.05$, its sign changes at $Z=1/3$. Simultaneously the coherent bandwidth is $ZW$: decreasing $Z$ does not supply an unlimited transition-temperature gain. The published argument explicitly allows deviations near the Mott boundary; its underlying DMFT model uses an infinite-coordination Bethe lattice. No self-consistent DMFT calculation or measured transition follows from this toy sweep. [R5](#ref-source-e2b9d469a7c556df)\n\n## Experimental criteria\n\nFor fcc Cs₃C₆₀, Ganin and colleagues report a pressure-dependent magnetic onset: 25.6 K at 1.3 kbar has only about 0.1% shielding, whereas 29.7 K at 2.2 kbar has about 12%. The maximum is approximately 35 K near 7 kbar, equivalent to 0.7 GPa. Measurements use 20 Oe, zero-field-cooled/field-cooled protocols and a tin pressure reference. A15 Cs₃C₆₀ reaches a separately reported maximum near 38 K; its value must not be assigned to the fcc sample. [R3](#ref-source-634d02f3c2bfde0d) [R4](#ref-source-5e6d3e7ed715ad6a)\n\nThe fcc study also separates magnetic ordering near 2.2 K from the A15 ordering scale near 46 K. Neither is a superconducting transition. Multiphase powders and small shielding fractions require particular care when locating the first superconducting signal. The magnetometry pressure range ends near 10.6 kbar; the separate diffraction measurements extend to much higher pressures. Combining those ranges would falsely imply that superconductivity was measured throughout the structural experiment. [R4](#ref-source-5e6d3e7ed715ad6a)\n\nPublished online on 9 June 2026, Shchukin and colleagues tune Rb uptake in nanostructured C₆₀ films. Figure 2f labels Rb₂.₇₁C₆₀ with $T_{\\mathrm{onset}}=22.4$ K and $T_{\\mathrm{zero}}=7.0$ K, and Rb₂.₉₈C₆₀ with 26.4 K and 14.5 K. The former criterion is a local resistivity maximum; the latter uses $d\\rho/dT<5\\times10^{-4}$ mΩ cm K⁻¹ in the plotted low-temperature window. It is a stated operational criterion, not an instrument-independent definition of exact zero resistance. [R8](#ref-source-64cd48d99353501a)\n\nThat experiment uses Raman analysis with relative scattering cross sections to estimate composition, and van der Pauw transport. The 10 μA intercalation current differs from the 1 μA resistance-probe current. Stoichiometry, grain connectivity, thickness and transition criterion must accompany any comparison with bulk rubidium fullerides. The supplement and underlying transport datasets have not been independently reanalyzed here. [R8](#ref-source-64cd48d99353501a)\n\n## Limits and disputes\n\nMitrano's optical study and Budden's longer-lived driven response concern pumped K₃C₆₀. A finite-frequency inductive response and suppressed transient resistance constrain the nonequilibrium state, but do not by themselves establish an equilibrium thermodynamic transition. Budden's final Figure 4 separates two measurements at a 100 K base temperature and approximately 25 mJ cm⁻² pump fluence:\n\n| Measurement | What the reported value means |\n|---|---|\n| Optical, Fig. 4a; 200 ps pump | Zero-frequency resistivity extrapolated from a Drude–Lorentz fit to transient optical conductivity; error bars reflect the fit confidence interval. |\n| Electrical, Fig. 4b; 75 ps pump | Transient two-terminal resistance after contact correction from a separate static four-terminal measurement; the shaded band estimates calibration error. |\n\nThe electrical readout uses a 1 ns voltage probe pulse. The corrected resistance is compatible with zero within the stated calibration uncertainty, and recovers on a tens-of-nanoseconds timescale. This supports the authors' assignment of a metastable superconducting state; it does not turn the 100 K measurement condition into an equilibrium Tc. Neither the pump duration nor the probe duration is the state lifetime. Both records retain `transient-response` temperatures with no equilibrium Tc. Complete supplement review, raw-data refitting and comparison of alternative conductivity models remain open. [R6](#ref-source-6ee3670220e24ff1) [R7](#ref-source-07be806c0002c690)\n\nThe historical hole-doped C₆₀ claim at 52 K was retracted on 6 March 2003. The original paper and its notice are retained together for traceability; the withdrawn value is excluded from experimental transition records. The notice identifies concerns about device-measurement data following an independent investigation. A citation in an older, otherwise valid paper does not restore the withdrawn claim. [R9](#ref-source-091fb85b144daad9) [R10](#ref-source-8822fee6435cf8cc)\n\n## Discovery implications\n\nFullerides motivate simultaneous control of bandwidth, local vibronic interactions, molecular valence and disorder. A superconducting dome near a Mott state is compatible with cooperation between phonons and correlations; it does not uniquely determine the pairing kernel. Neither a fully open gap nor proximity to a magnetic insulator proves that one interaction acts alone. Report model assumptions beside the experimental evidence used to constrain them. [R4](#ref-source-5e6d3e7ed715ad6a) [R5](#ref-source-e2b9d469a7c556df)\n\nCurrent-driven intercalation offers a method for tuning samples rather than a new bulk temperature record. Reproducible optimization needs composition maps, measurement-current controls and comparable transition definitions. Keep pressure polymorphs and optically driven states separate when selecting targets: their conditions cannot be collapsed into a single family-wide Tc ranking. [R8](#ref-source-64cd48d99353501a) [R4](#ref-source-5e6d3e7ed715ad6a) [R7](#ref-source-07be806c0002c690)\n\n## Related topics\n\nContinue with [electron–phonon pairing](/scwiki/bcs-weak-coupling), [Eliashberg theory](/scwiki/eliashberg-strong-coupling), [Mottness](/scwiki/mottness-and-superconductivity), [s-wave pairing](/scwiki/s-wave) and [zero resistance and driven-state evidence](/scwiki/zero-resistance).","revision":"2da5142890f83dc4f172","sections":[{"id":"scope","title":"Scope","markdown":"## Scope\n\nAlkali-doped fullerides combine molecular vibrations, narrow electronic bands and strong local interactions. Ideal A₃C₆₀ has three donated electrons in a molecular t₁ᵤ manifold with six spin-orbital states: half-filling describes electron counting, not a guarantee of metallic transport or superconductivity. The same nominal Cs₃C₆₀ composition supports fcc and A15 packings with different magnetic and pressure-dependent superconducting behavior. Specify composition, structure, preparation and measurement conditions before comparing temperatures. Pressure-induced equilibrium superconductivity and optically driven responses are separate evidence classes. [R5](#ref-source-e2b9d469a7c556df) [R4](#ref-source-5e6d3e7ed715ad6a) [R7](#ref-source-07be806c0002c690)\n\nNominal composition is not a sample assay. Ganin's fcc-rich powder had refined composition Cs₂.₉₀₁₍₆₎C₆₀ and an fcc fraction of about 86%, with minority phases. Its ambient-pressure magnetic insulating behavior illustrates why three donated electrons alone cannot define the phase. These preparation and phase-fraction qualifications accompany the idealized A₃C₆₀ description. [R4](#ref-source-5e6d3e7ed715ad6a)\n\nThe 1991 potassium discovery already illustrates why one temperature is insufficient: the abstract reports a thin-film resistive onset near 16 K and essentially vanishing resistance by 5 K, while bulk magnetic and microwave measurements indicate an 18 K transition. The subsequent rubidium report gives a maximum of 28 K from bulk magnetic and microwave evidence. These abstract-level checks establish historical observations; they do not constitute a complete reassessment of the original specimens. [R1](#ref-source-51b1a52d16139e58) [R2](#ref-source-0fb5ae1290bd2998)"},{"id":"mathematical-assumptions","title":"Mathematical assumptions","markdown":"## Mathematical assumptions\n\nOne influential model represents each molecule by three effective p-like orbitals with local terms $H_U=U(n-3)^2/2$ and $H_J=J[2\\mathbf S^2+\\mathbf L^2/2]+5J(n-3)^2/6$. Angular momenta are dimensionless. In this convention ordinary Hund exchange has $J=-J_H<0$; integrating out Jahn–Teller vibrations can instead give $J=-J_H+J_{JT}>0$. This static reduction requires the coherent electronic scale $ZW$ to lie below the relevant phonon energy. It should not be applied across the whole bandwidth range without checking retardation. [R5](#ref-source-e2b9d469a7c556df)\n\nAt exactly three electrons, the model multiplets $^4S$, $^2D$ and $^2P$ have energies $15J/2$, $9J/2$ and $5J/2$, with respective degeneracies 4, 10 and 6. They account for $\\binom{6}{3}=20$ local states. Positive effective $J$ favors the low-spin $^2P$ multiplet; negative $J$ favors $^4S$. This is an algebraic check of the effective local Hamiltonian, not a measured molecular spectrum or proof of superconducting order. [R5](#ref-source-e2b9d469a7c556df)\n\nThe heuristic Cooper-channel amplitude $A^*\\simeq ZU-10J/3$ illustrates how correlations can reduce repulsion relative to an inverted exchange. For illustrative fixed ratios $U/W=0.5$ and $J/W=0.05$, its sign changes at $Z=1/3$. Simultaneously the coherent bandwidth is $ZW$: decreasing $Z$ does not supply an unlimited transition-temperature gain. The published argument explicitly allows deviations near the Mott boundary; its underlying DMFT model uses an infinite-coordination Bethe lattice. No self-consistent DMFT calculation or measured transition follows from this toy sweep. [R5](#ref-source-e2b9d469a7c556df)"},{"id":"experimental-criteria","title":"Experimental criteria","markdown":"## Experimental criteria\n\nFor fcc Cs₃C₆₀, Ganin and colleagues report a pressure-dependent magnetic onset: 25.6 K at 1.3 kbar has only about 0.1% shielding, whereas 29.7 K at 2.2 kbar has about 12%. The maximum is approximately 35 K near 7 kbar, equivalent to 0.7 GPa. Measurements use 20 Oe, zero-field-cooled/field-cooled protocols and a tin pressure reference. A15 Cs₃C₆₀ reaches a separately reported maximum near 38 K; its value must not be assigned to the fcc sample. [R3](#ref-source-634d02f3c2bfde0d) [R4](#ref-source-5e6d3e7ed715ad6a)\n\nThe fcc study also separates magnetic ordering near 2.2 K from the A15 ordering scale near 46 K. Neither is a superconducting transition. Multiphase powders and small shielding fractions require particular care when locating the first superconducting signal. The magnetometry pressure range ends near 10.6 kbar; the separate diffraction measurements extend to much higher pressures. Combining those ranges would falsely imply that superconductivity was measured throughout the structural experiment. [R4](#ref-source-5e6d3e7ed715ad6a)\n\nPublished online on 9 June 2026, Shchukin and colleagues tune Rb uptake in nanostructured C₆₀ films. Figure 2f labels Rb₂.₇₁C₆₀ with $T_{\\mathrm{onset}}=22.4$ K and $T_{\\mathrm{zero}}=7.0$ K, and Rb₂.₉₈C₆₀ with 26.4 K and 14.5 K. The former criterion is a local resistivity maximum; the latter uses $d\\rho/dT<5\\times10^{-4}$ mΩ cm K⁻¹ in the plotted low-temperature window. It is a stated operational criterion, not an instrument-independent definition of exact zero resistance. [R8](#ref-source-64cd48d99353501a)\n\nThat experiment uses Raman analysis with relative scattering cross sections to estimate composition, and van der Pauw transport. The 10 μA intercalation current differs from the 1 μA resistance-probe current. Stoichiometry, grain connectivity, thickness and transition criterion must accompany any comparison with bulk rubidium fullerides. The supplement and underlying transport datasets have not been independently reanalyzed here. [R8](#ref-source-64cd48d99353501a)"},{"id":"limits-and-disputes","title":"Limits and disputes","markdown":"## Limits and disputes\n\nMitrano's optical study and Budden's longer-lived driven response concern pumped K₃C₆₀. A finite-frequency inductive response and suppressed transient resistance constrain the nonequilibrium state, but do not by themselves establish an equilibrium thermodynamic transition. Budden's final Figure 4 separates two measurements at a 100 K base temperature and approximately 25 mJ cm⁻² pump fluence:\n\n| Measurement | What the reported value means |\n|---|---|\n| Optical, Fig. 4a; 200 ps pump | Zero-frequency resistivity extrapolated from a Drude–Lorentz fit to transient optical conductivity; error bars reflect the fit confidence interval. |\n| Electrical, Fig. 4b; 75 ps pump | Transient two-terminal resistance after contact correction from a separate static four-terminal measurement; the shaded band estimates calibration error. |\n\nThe electrical readout uses a 1 ns voltage probe pulse. The corrected resistance is compatible with zero within the stated calibration uncertainty, and recovers on a tens-of-nanoseconds timescale. This supports the authors' assignment of a metastable superconducting state; it does not turn the 100 K measurement condition into an equilibrium Tc. Neither the pump duration nor the probe duration is the state lifetime. Both records retain `transient-response` temperatures with no equilibrium Tc. Complete supplement review, raw-data refitting and comparison of alternative conductivity models remain open. [R6](#ref-source-6ee3670220e24ff1) [R7](#ref-source-07be806c0002c690)\n\nThe historical hole-doped C₆₀ claim at 52 K was retracted on 6 March 2003. The original paper and its notice are retained together for traceability; the withdrawn value is excluded from experimental transition records. The notice identifies concerns about device-measurement data following an independent investigation. A citation in an older, otherwise valid paper does not restore the withdrawn claim. [R9](#ref-source-091fb85b144daad9) [R10](#ref-source-8822fee6435cf8cc)"},{"id":"discovery-implications","title":"Discovery implications","markdown":"## Discovery implications\n\nFullerides motivate simultaneous control of bandwidth, local vibronic interactions, molecular valence and disorder. A superconducting dome near a Mott state is compatible with cooperation between phonons and correlations; it does not uniquely determine the pairing kernel. Neither a fully open gap nor proximity to a magnetic insulator proves that one interaction acts alone. Report model assumptions beside the experimental evidence used to constrain them. [R4](#ref-source-5e6d3e7ed715ad6a) [R5](#ref-source-e2b9d469a7c556df)\n\nCurrent-driven intercalation offers a method for tuning samples rather than a new bulk temperature record. Reproducible optimization needs composition maps, measurement-current controls and comparable transition definitions. Keep pressure polymorphs and optically driven states separate when selecting targets: their conditions cannot be collapsed into a single family-wide Tc ranking. [R8](#ref-source-64cd48d99353501a) [R4](#ref-source-5e6d3e7ed715ad6a) [R7](#ref-source-07be806c0002c690)"},{"id":"related-topics","title":"Related topics","markdown":"## Related topics\n\nContinue with [electron–phonon pairing](/scwiki/bcs-weak-coupling), [Eliashberg theory](/scwiki/eliashberg-strong-coupling), [Mottness](/scwiki/mottness-and-superconductivity), [s-wave pairing](/scwiki/s-wave) and [zero resistance and driven-state evidence](/scwiki/zero-resistance)."},{"id":"material-cases","title":"Material cases","markdown":"## Material cases\n\nValues describe individual reports, not a ranking. Unknown means the checked source did not supply the field at this review scope.\n\n| Material and sample | Reported temperature | Criterion | Probe | Pressure | State | Evidence |\n|---|---|---|---|---|---|---|\n| K-doped C60 (aliases: fulleride, fullerides); Hebard bulk specimen | 18 K; Original abstract only; film 16 K onset / 5 K essentially zero are different measurements. | transition; magnetic-and-microwave-onset | Meissner and microwave response | ambient; unknown GPa | equilibrium | experiment; [source](#ref-source-51b1a52d16139e58) |\n| RbxC60 (aliases: fulleride, fullerides); Rosseinsky bulk discovery material | 28 K; Reported maximum; full original methods not reviewed. | transition; magnetic-and-microwave-onset | Meissner and microwave response | ambient; unknown GPa | equilibrium | experiment; [source](#ref-source-0fb5ae1290bd2998) |\n| Cs3C60 (aliases: fulleride, fullerides); fcc polymorph, trace shielding | 25.6 K; About 0.1% shielding; do not infer bulk fraction from this onset. | transition; magnetization-onset-trace-shielding | 20 Oe ZFC/FC magnetometry | high; 0.13 to 0.13 GPa | equilibrium | experiment; [source](#ref-source-5e6d3e7ed715ad6a) |\n| Cs3C60 (aliases: fulleride, fullerides); fcc polymorph, about 12% shielding | 29.7 K; Pressure-specific magnetic onset in a multiphase powder. | transition; magnetization-onset | 20 Oe ZFC/FC magnetometry | high; 0.22 to 0.22 GPa | equilibrium | experiment; [source](#ref-source-5e6d3e7ed715ad6a) |\n| Cs3C60 (aliases: fulleride, fullerides); fcc polymorph dome maximum | 35 K; Approximate maximum at approximately 7 kbar; not A15 maximum 38 K. | transition; magnetization-onset | 20 Oe ZFC/FC magnetometry | high; 0.7 to 0.7 GPa | equilibrium | experiment; [source](#ref-source-5e6d3e7ed715ad6a) |\n| Cs3C60 (aliases: fulleride, fullerides); fcc ambient-pressure magnetic ordering | 2.2 K; Magnetic ordering, not a superconducting Tc. | measurement; magnetic-ordering-temperature | Muon spin rotation and magnetism | ambient; unknown GPa | equilibrium | experiment; [source](#ref-source-5e6d3e7ed715ad6a) |\n| Rb2.98C60 (aliases: fulleride, fullerides); Shchukin nanostructured film, Fig2f onset | 26.4 K; Same film as 14.5 K derivative-threshold record; two criteria, not two independent specimens. | transition; local-resistivity-maximum | Van der Pauw transport, 1 μA | ambient; unknown GPa | equilibrium | experiment; [source](#ref-source-64cd48d99353501a) |\n| Rb2.98C60 (aliases: fulleride, fullerides); Shchukin nanostructured film, Fig2f low-temperature threshold | 14.5 K; Tzero defined by dρ/dT<5e-4 mΩcm/K in plotted window; not instrument-independent exact zero. | transition; resistivity-derivative-threshold | Van der Pauw transport, 1 μA | ambient; unknown GPa | equilibrium | experiment; [source](#ref-source-64cd48d99353501a) |\n| Rb2.71C60 (aliases: fulleride, fullerides); Shchukin nanostructured film, Fig2f low-temperature threshold | 7 K; Same operational derivative threshold as 14.5 K optimally intercalated film. | transition; resistivity-derivative-threshold | Van der Pauw transport, 1 μA | ambient; unknown GPa | equilibrium | experiment; [source](#ref-source-64cd48d99353501a) |\n| K3C60 (aliases: fulleride, fullerides); Budden final Fig.4b optically driven K3C60 pellet | 100 K; 100K base; approximately25mJ/cm2 fluence and75ps pump. Contact-corrected resistance compatible with zero within calibration uncertainty. Transient recovery is not an equilibrium transition; pump/probe duration is not lifetime. | transient-response; driven-resistance-suppression | Transient two-terminal transport;1ns voltage probe; static four-terminal contact calibration | ambient; unknown GPa | transient | experiment; [source](#ref-source-07be806c0002c690) |\n| K3C60 (aliases: fulleride, fullerides); Budden final Fig.4a optically driven K3C60 optical measurement | 100 K; 100K base; approximately25mJ/cm2 fluence and200ps pump. Error bars are fit confidence intervals. Extrapolated transient resistivity is not a direct equilibrium DC transport measurement or equilibrium Tc. | transient-response; driven-optical-zero-frequency-extrapolation | Drude-Lorentz fit to transient optical conductivity, extrapolated to zero frequency | ambient; unknown GPa | transient | experiment; [source](#ref-source-07be806c0002c690) |"}],"markdown":"# Fulleride superconductors: Jahn–Teller coupling, Mott physics and driven states\n\nCompare alkali-doped C60 compounds through pressure, molecular interactions and sample-specific transition criteria, with explicit boundaries for driven and retracted claims.\n\n## Scope\n\nAlkali-doped fullerides combine molecular vibrations, narrow electronic bands and strong local interactions. Ideal A₃C₆₀ has three donated electrons in a molecular t₁ᵤ manifold with six spin-orbital states: half-filling describes electron counting, not a guarantee of metallic transport or superconductivity. The same nominal Cs₃C₆₀ composition supports fcc and A15 packings with different magnetic and pressure-dependent superconducting behavior. Specify composition, structure, preparation and measurement conditions before comparing temperatures. Pressure-induced equilibrium superconductivity and optically driven responses are separate evidence classes. [R5](#ref-source-e2b9d469a7c556df) [R4](#ref-source-5e6d3e7ed715ad6a) [R7](#ref-source-07be806c0002c690)\n\nNominal composition is not a sample assay. Ganin's fcc-rich powder had refined composition Cs₂.₉₀₁₍₆₎C₆₀ and an fcc fraction of about 86%, with minority phases. Its ambient-pressure magnetic insulating behavior illustrates why three donated electrons alone cannot define the phase. These preparation and phase-fraction qualifications accompany the idealized A₃C₆₀ description. [R4](#ref-source-5e6d3e7ed715ad6a)\n\nThe 1991 potassium discovery already illustrates why one temperature is insufficient: the abstract reports a thin-film resistive onset near 16 K and essentially vanishing resistance by 5 K, while bulk magnetic and microwave measurements indicate an 18 K transition. The subsequent rubidium report gives a maximum of 28 K from bulk magnetic and microwave evidence. These abstract-level checks establish historical observations; they do not constitute a complete reassessment of the original specimens. [R1](#ref-source-51b1a52d16139e58) [R2](#ref-source-0fb5ae1290bd2998)\n\n## Mathematical assumptions\n\nOne influential model represents each molecule by three effective p-like orbitals with local terms $H_U=U(n-3)^2/2$ and $H_J=J[2\\mathbf S^2+\\mathbf L^2/2]+5J(n-3)^2/6$. Angular momenta are dimensionless. In this convention ordinary Hund exchange has $J=-J_H<0$; integrating out Jahn–Teller vibrations can instead give $J=-J_H+J_{JT}>0$. This static reduction requires the coherent electronic scale $ZW$ to lie below the relevant phonon energy. It should not be applied across the whole bandwidth range without checking retardation. [R5](#ref-source-e2b9d469a7c556df)\n\nAt exactly three electrons, the model multiplets $^4S$, $^2D$ and $^2P$ have energies $15J/2$, $9J/2$ and $5J/2$, with respective degeneracies 4, 10 and 6. They account for $\\binom{6}{3}=20$ local states. Positive effective $J$ favors the low-spin $^2P$ multiplet; negative $J$ favors $^4S$. This is an algebraic check of the effective local Hamiltonian, not a measured molecular spectrum or proof of superconducting order. [R5](#ref-source-e2b9d469a7c556df)\n\nThe heuristic Cooper-channel amplitude $A^*\\simeq ZU-10J/3$ illustrates how correlations can reduce repulsion relative to an inverted exchange. For illustrative fixed ratios $U/W=0.5$ and $J/W=0.05$, its sign changes at $Z=1/3$. Simultaneously the coherent bandwidth is $ZW$: decreasing $Z$ does not supply an unlimited transition-temperature gain. The published argument explicitly allows deviations near the Mott boundary; its underlying DMFT model uses an infinite-coordination Bethe lattice. No self-consistent DMFT calculation or measured transition follows from this toy sweep. [R5](#ref-source-e2b9d469a7c556df)\n\n## Experimental criteria\n\nFor fcc Cs₃C₆₀, Ganin and colleagues report a pressure-dependent magnetic onset: 25.6 K at 1.3 kbar has only about 0.1% shielding, whereas 29.7 K at 2.2 kbar has about 12%. The maximum is approximately 35 K near 7 kbar, equivalent to 0.7 GPa. Measurements use 20 Oe, zero-field-cooled/field-cooled protocols and a tin pressure reference. A15 Cs₃C₆₀ reaches a separately reported maximum near 38 K; its value must not be assigned to the fcc sample. [R3](#ref-source-634d02f3c2bfde0d) [R4](#ref-source-5e6d3e7ed715ad6a)\n\nThe fcc study also separates magnetic ordering near 2.2 K from the A15 ordering scale near 46 K. Neither is a superconducting transition. Multiphase powders and small shielding fractions require particular care when locating the first superconducting signal. The magnetometry pressure range ends near 10.6 kbar; the separate diffraction measurements extend to much higher pressures. Combining those ranges would falsely imply that superconductivity was measured throughout the structural experiment. [R4](#ref-source-5e6d3e7ed715ad6a)\n\nPublished online on 9 June 2026, Shchukin and colleagues tune Rb uptake in nanostructured C₆₀ films. Figure 2f labels Rb₂.₇₁C₆₀ with $T_{\\mathrm{onset}}=22.4$ K and $T_{\\mathrm{zero}}=7.0$ K, and Rb₂.₉₈C₆₀ with 26.4 K and 14.5 K. The former criterion is a local resistivity maximum; the latter uses $d\\rho/dT<5\\times10^{-4}$ mΩ cm K⁻¹ in the plotted low-temperature window. It is a stated operational criterion, not an instrument-independent definition of exact zero resistance. [R8](#ref-source-64cd48d99353501a)\n\nThat experiment uses Raman analysis with relative scattering cross sections to estimate composition, and van der Pauw transport. The 10 μA intercalation current differs from the 1 μA resistance-probe current. Stoichiometry, grain connectivity, thickness and transition criterion must accompany any comparison with bulk rubidium fullerides. The supplement and underlying transport datasets have not been independently reanalyzed here. [R8](#ref-source-64cd48d99353501a)\n\n## Limits and disputes\n\nMitrano's optical study and Budden's longer-lived driven response concern pumped K₃C₆₀. A finite-frequency inductive response and suppressed transient resistance constrain the nonequilibrium state, but do not by themselves establish an equilibrium thermodynamic transition. Budden's final Figure 4 separates two measurements at a 100 K base temperature and approximately 25 mJ cm⁻² pump fluence:\n\n| Measurement | What the reported value means |\n|---|---|\n| Optical, Fig. 4a; 200 ps pump | Zero-frequency resistivity extrapolated from a Drude–Lorentz fit to transient optical conductivity; error bars reflect the fit confidence interval. |\n| Electrical, Fig. 4b; 75 ps pump | Transient two-terminal resistance after contact correction from a separate static four-terminal measurement; the shaded band estimates calibration error. |\n\nThe electrical readout uses a 1 ns voltage probe pulse. The corrected resistance is compatible with zero within the stated calibration uncertainty, and recovers on a tens-of-nanoseconds timescale. This supports the authors' assignment of a metastable superconducting state; it does not turn the 100 K measurement condition into an equilibrium Tc. Neither the pump duration nor the probe duration is the state lifetime. Both records retain `transient-response` temperatures with no equilibrium Tc. Complete supplement review, raw-data refitting and comparison of alternative conductivity models remain open. [R6](#ref-source-6ee3670220e24ff1) [R7](#ref-source-07be806c0002c690)\n\nThe historical hole-doped C₆₀ claim at 52 K was retracted on 6 March 2003. The original paper and its notice are retained together for traceability; the withdrawn value is excluded from experimental transition records. The notice identifies concerns about device-measurement data following an independent investigation. A citation in an older, otherwise valid paper does not restore the withdrawn claim. [R9](#ref-source-091fb85b144daad9) [R10](#ref-source-8822fee6435cf8cc)\n\n## Discovery implications\n\nFullerides motivate simultaneous control of bandwidth, local vibronic interactions, molecular valence and disorder. A superconducting dome near a Mott state is compatible with cooperation between phonons and correlations; it does not uniquely determine the pairing kernel. Neither a fully open gap nor proximity to a magnetic insulator proves that one interaction acts alone. Report model assumptions beside the experimental evidence used to constrain them. [R4](#ref-source-5e6d3e7ed715ad6a) [R5](#ref-source-e2b9d469a7c556df)\n\nCurrent-driven intercalation offers a method for tuning samples rather than a new bulk temperature record. Reproducible optimization needs composition maps, measurement-current controls and comparable transition definitions. Keep pressure polymorphs and optically driven states separate when selecting targets: their conditions cannot be collapsed into a single family-wide Tc ranking. [R8](#ref-source-64cd48d99353501a) [R4](#ref-source-5e6d3e7ed715ad6a) [R7](#ref-source-07be806c0002c690)\n\n## Related topics\n\nContinue with [electron–phonon pairing](/scwiki/bcs-weak-coupling), [Eliashberg theory](/scwiki/eliashberg-strong-coupling), [Mottness](/scwiki/mottness-and-superconductivity), [s-wave pairing](/scwiki/s-wave) and [zero resistance and driven-state evidence](/scwiki/zero-resistance).\n\n## Material cases\n\nValues describe individual reports, not a ranking. Unknown means the checked source did not supply the field at this review scope.\n\n| Material and sample | Reported temperature | Criterion | Probe | Pressure | State | Evidence |\n|---|---|---|---|---|---|---|\n| K-doped C60 (aliases: fulleride, fullerides); Hebard bulk specimen | 18 K; Original abstract only; film 16 K onset / 5 K essentially zero are different measurements. | transition; magnetic-and-microwave-onset | Meissner and microwave response | ambient; unknown GPa | equilibrium | experiment; [source](#ref-source-51b1a52d16139e58) |\n| RbxC60 (aliases: fulleride, fullerides); Rosseinsky bulk discovery material | 28 K; Reported maximum; full original methods not reviewed. | transition; magnetic-and-microwave-onset | Meissner and microwave response | ambient; unknown GPa | equilibrium | experiment; [source](#ref-source-0fb5ae1290bd2998) |\n| Cs3C60 (aliases: fulleride, fullerides); fcc polymorph, trace shielding | 25.6 K; About 0.1% shielding; do not infer bulk fraction from this onset. | transition; magnetization-onset-trace-shielding | 20 Oe ZFC/FC magnetometry | high; 0.13 to 0.13 GPa | equilibrium | experiment; [source](#ref-source-5e6d3e7ed715ad6a) |\n| Cs3C60 (aliases: fulleride, fullerides); fcc polymorph, about 12% shielding | 29.7 K; Pressure-specific magnetic onset in a multiphase powder. | transition; magnetization-onset | 20 Oe ZFC/FC magnetometry | high; 0.22 to 0.22 GPa | equilibrium | experiment; [source](#ref-source-5e6d3e7ed715ad6a) |\n| Cs3C60 (aliases: fulleride, fullerides); fcc polymorph dome maximum | 35 K; Approximate maximum at approximately 7 kbar; not A15 maximum 38 K. | transition; magnetization-onset | 20 Oe ZFC/FC magnetometry | high; 0.7 to 0.7 GPa | equilibrium | experiment; [source](#ref-source-5e6d3e7ed715ad6a) |\n| Cs3C60 (aliases: fulleride, fullerides); fcc ambient-pressure magnetic ordering | 2.2 K; Magnetic ordering, not a superconducting Tc. | measurement; magnetic-ordering-temperature | Muon spin rotation and magnetism | ambient; unknown GPa | equilibrium | experiment; [source](#ref-source-5e6d3e7ed715ad6a) |\n| Rb2.98C60 (aliases: fulleride, fullerides); Shchukin nanostructured film, Fig2f onset | 26.4 K; Same film as 14.5 K derivative-threshold record; two criteria, not two independent specimens. | transition; local-resistivity-maximum | Van der Pauw transport, 1 μA | ambient; unknown GPa | equilibrium | experiment; [source](#ref-source-64cd48d99353501a) |\n| Rb2.98C60 (aliases: fulleride, fullerides); Shchukin nanostructured film, Fig2f low-temperature threshold | 14.5 K; Tzero defined by dρ/dT<5e-4 mΩcm/K in plotted window; not instrument-independent exact zero. | transition; resistivity-derivative-threshold | Van der Pauw transport, 1 μA | ambient; unknown GPa | equilibrium | experiment; [source](#ref-source-64cd48d99353501a) |\n| Rb2.71C60 (aliases: fulleride, fullerides); Shchukin nanostructured film, Fig2f low-temperature threshold | 7 K; Same operational derivative threshold as 14.5 K optimally intercalated film. | transition; resistivity-derivative-threshold | Van der Pauw transport, 1 μA | ambient; unknown GPa | equilibrium | experiment; [source](#ref-source-64cd48d99353501a) |\n| K3C60 (aliases: fulleride, fullerides); Budden final Fig.4b optically driven K3C60 pellet | 100 K; 100K base; approximately25mJ/cm2 fluence and75ps pump. Contact-corrected resistance compatible with zero within calibration uncertainty. Transient recovery is not an equilibrium transition; pump/probe duration is not lifetime. | transient-response; driven-resistance-suppression | Transient two-terminal transport;1ns voltage probe; static four-terminal contact calibration | ambient; unknown GPa | transient | experiment; [source](#ref-source-07be806c0002c690) |\n| K3C60 (aliases: fulleride, fullerides); Budden final Fig.4a optically driven K3C60 optical measurement | 100 K; 100K base; approximately25mJ/cm2 fluence and200ps pump. Error bars are fit confidence intervals. Extrapolated transient resistivity is not a direct equilibrium DC transport measurement or equilibrium Tc. | transient-response; driven-optical-zero-frequency-extrapolation | Drude-Lorentz fit to transient optical conductivity, extrapolated to zero frequency | ambient; unknown GPa | transient | experiment; [source](#ref-source-07be806c0002c690) |\n\n## Sources\n\n### Ref source-51b1a52d16139e58\n\n[R1] Superconductivity at 18 K in potassium-doped C60 (1991). [DOI 10.1038/350600a0](https://doi.org/10.1038/350600a0). Publication: journal-article. Check: original-abstract-check. Checked: 2026-10-18. Original abstract distinguishes film resistive onset16K/essentially zero5K from bulk magnetic/microwave18K. Full PDF returned403; full experimental methods not reviewed.\n### Ref source-0fb5ae1290bd2998\n\n[R2] Superconductivity at 28 K in RbxC60 (1991). [DOI 10.1103/PhysRevLett.66.2830](https://doi.org/10.1103/PhysRevLett.66.2830). Publication: journal-article. Check: publisher-abstract-check. Checked: 2026-10-18. Published27May1991. Original abstract checked for bulk Meissner/microwave maximum28K. Full methods not reviewed; title stoichiometry remains RbxC60.\n### Ref source-634d02f3c2bfde0d\n\n[R3] Bulk superconductivity at 38 K in a molecular system (2008). [DOI 10.1038/nmat2179](https://doi.org/10.1038/nmat2179). Publication: journal-article. Check: publisher-metadata-and-later-primary-comparison. Checked: 2026-10-18. Online20April2008. Metadata checked and A15 maximum38K cross-checked against Ganin2010 original comparison. Direct PDF response was not a PDF; full original methods not reviewed.\n### Ref source-5e6d3e7ed715ad6a\n\n[R4] Polymorphism control of superconductivity and magnetism in Cs3C60 close to the Mott transition (2010). [DOI 10.1038/nature09120](https://doi.org/10.1038/nature09120). Publication: journal-article. Check: selected-published-pressure-magnetism-methods. Checked: 2026-10-20. Original Nature466,221–225, issue8July2010, hosted as an unchanged paper PDF. Selected pp221–222, Fig3 caption p224 and online magnetic Methods read; p222 visually inspected. Multiphase sample, pressure calibration and shielding criteria retained. Complete supplement and raw data not reanalyzed. Follow-up selected published p.221: refined Cs2.901(6)C60, about86%fcc fraction, minority phases and ambient-pressure magnetic insulating behavior; not a new whole-paper review.\n### Ref source-e2b9d469a7c556df\n\n[R5] Colloquium: Modeling the unconventional superconducting properties of expanded A3C60 fullerides (2009). [DOI 10.1103/RevModPhys.81.943](https://doi.org/10.1103/RevModPhys.81.943). Publication: journal-article. Check: selected-author-model-equations-check. Checked: 2026-10-20. Authorv1 submitted4September2008; journal19June2009. Selected p5 Eq1–3, p8 model discussion and p9 heuristic Cooper amplitude read; p5 visually inspected. Independent n=3 multiplets and illustrative amplitude/unit checks, not a DMFT reproduction. Final-version comparison and complete review remain open. Follow-up author-v1 p.2 introduction: three donated electrons half-fill the molecular t1u manifold; this count alone does not establish the electronic phase.\n### Ref source-6ee3670220e24ff1\n\n[R6] Possible light-induced superconductivity in K3C60 at high temperature (2016). [DOI 10.1038/nature16522](https://doi.org/10.1038/nature16522). Publication: journal-article. Check: earlier-author-manuscript-scoped-check. Checked: 2026-10-19. Reused B7/A1 scoped primary reading, with the same version and methods limitations. Inherited A1 selected pp.1–2,4–6 check: finite-window transient optical response and high-mobility alternative. The publisher’s 24 February 2016 caption-correction notice is identified; no full final-version equivalence is established.\n### Ref source-07be806c0002c690\n\n[R7] Evidence for metastable photo-induced superconductivity in K3C60 (2021). [DOI 10.1038/s41567-020-01148-1](https://doi.org/10.1038/s41567-020-01148-1). Publication: journal-article. Check: selected-final-figure-and-transport-calibration. Checked: 2026-10-20. Cached final published paper p.615 Fig.4/caption and text read; figure pixels visually inspected.200ps optical and75ps transport pumps at100K,approximately25mJ/cm2; optical zero-frequency extrapolation versus transient two-terminal contact-calibrated resistance and1ns voltage probe. Supersedes earlier-manuscript-only scope for these passages. Web refetch returned403; cached final artifact retained. Complete supplement, raw-data refit and full author/final version comparison remain open.\n### Ref source-64cd48d99353501a\n\n[R8] On-Chip Tuning of Superconductivity in Fullerides via Current-Driven Rb+ Intercalation (2026). [DOI 10.1021/acsnano.6c02466](https://doi.org/10.1021/acsnano.6c02466). Publication: journal-article. Check: selected-published-transport-and-composition-methods. Checked: 2026-10-18. Publishedonline9June2026, not repository upload29June; issue23June. Selected pp17360–17363 and electrical transport/EPC passages pp17367–17368 read. Fig2f p17362 visually inspected for separate onset and derivative-threshold temperatures. Supplement and original datasets not reanalyzed.\n### Ref source-091fb85b144daad9\n\n[R9] RETRACTED ARTICLE: Superconductivity at 52 K in hole-doped C60 (2000). [DOI 10.1038/35046008](https://doi.org/10.1038/35046008). Publication: journal-article. Retracted: 2003-03-06. [Retraction notice](https://doi.org/10.1038/nature01466). Check: retracted-article-identity-check. Checked: 2026-10-18. Original30November2000 identity and retraction link checked; withdrawn52K claim is not an experimental benchmark.\n### Ref source-8822fee6435cf8cc\n\n[R10] Retraction Note to: Superconductivity at 52 K in hole-doped C60 (2003). [DOI 10.1038/nature01466](https://doi.org/10.1038/nature01466). Publication: journal-article. Check: publisher-indexed-complete-notice-text. Checked: 2026-10-18. Published6March2003. Complete indexed notice text read and original DOI link verified; concerns concern device-measurement data after independent investigation. Direct publisher HTML identity redirect unavailable.\n\n## Claim evidence and conditions\n\n### scwiki-d9-claim-scope-1\n\nAlkali-doped fullerides combine molecular vibrations, narrow electronic bands and strong local interactions. Ideal A₃C₆₀ has three donated electrons in a molecular t₁ᵤ manifold with six spin-orbital states: half-filling describes electron counting, not a guarantee of metallic transport or superconductivity. The same nominal Cs₃C₆₀ composition supports fcc and A15 packings with different magnetic and pressure-dependent superconducting behavior. Specify composition, structure, preparation and measurement conditions before comparing temperatures. Pressure-induced equilibrium superconductivity and optically driven responses are separate evidence classes.\n\nNominal composition is not a sample assay. Ganin's fcc-rich powder had refined composition Cs₂.₉₀₁₍₆₎C₆₀ and an fcc fraction of about 86%, with minority phases. Its ambient-pressure magnetic insulating behavior illustrates why three donated electrons alone cannot define the phase. These preparation and phase-fraction qualifications accompany the idealized A₃C₆₀ description.\n\nEvidence: theory. Sources: source-e2b9d469a7c556df, source-5e6d3e7ed715ad6a, source-07be806c0002c690.\n\nSource relationship: mixed-source-and-local-derivation. Capone supplies the ideal molecular electron count; Ganin supplies the polymorph, refined composition and phase-fraction evidence; Budden supplies the driven experiment. Separating nominal filling, measured composition and equilibrium/driven evidence is editorial synthesis, not a new phase calculation.\n\nConditions: Ideal three-electron t1u manifold; actual fcc-rich Cs3C60 powder is multiphase, refined Cs2.901(6)C60. Pressure, polymorph, probe and optical excitation must remain attached.\n\nVerification scope: Selected Capone author-v1 introduction, Ganin published p.221 and Budden final p.615/Fig.4; not a full review or raw-data reproduction.\n\n### scwiki-d9-claim-scope-2\n\nThe 1991 potassium discovery already illustrates why one temperature is insufficient: the abstract reports a thin-film resistive onset near 16 K and essentially vanishing resistance by 5 K, while bulk magnetic and microwave measurements indicate an 18 K transition. The subsequent rubidium report gives a maximum of 28 K from bulk magnetic and microwave evidence. These abstract-level checks establish historical observations; they do not constitute a complete reassessment of the original specimens.\n\nEvidence: experiment. Sources: source-51b1a52d16139e58, source-0fb5ae1290bd2998.\n\nConditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.\n\nVerification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.\n\n### scwiki-d9-claim-mathematical-assumptions-1\n\nOne influential model represents each molecule by three effective p-like orbitals with local terms $H_U=U(n-3)^2/2$ and $H_J=J[2\\mathbf S^2+\\mathbf L^2/2]+5J(n-3)^2/6$. Angular momenta are dimensionless. In this convention ordinary Hund exchange has $J=-J_H<0$; integrating out Jahn–Teller vibrations can instead give $J=-J_H+J_{JT}>0$. This static reduction requires the coherent electronic scale $ZW$ to lie below the relevant phonon energy. It should not be applied across the whole bandwidth range without checking retardation.\n\nEvidence: theory. Sources: source-e2b9d469a7c556df.\n\nConditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.\n\nVerification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.\n\n### scwiki-d9-claim-mathematical-assumptions-2\n\nAt exactly three electrons, the model multiplets $^4S$, $^2D$ and $^2P$ have energies $15J/2$, $9J/2$ and $5J/2$, with respective degeneracies 4, 10 and 6. They account for $\\binom{6}{3}=20$ local states. Positive effective $J$ favors the low-spin $^2P$ multiplet; negative $J$ favors $^4S$. This is an algebraic check of the effective local Hamiltonian, not a measured molecular spectrum or proof of superconducting order.\n\nEvidence: theory. Sources: source-e2b9d469a7c556df.\n\nConditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.\n\nVerification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.\n\n### scwiki-d9-claim-mathematical-assumptions-3\n\nThe heuristic Cooper-channel amplitude $A^*\\simeq ZU-10J/3$ illustrates how correlations can reduce repulsion relative to an inverted exchange. For illustrative fixed ratios $U/W=0.5$ and $J/W=0.05$, its sign changes at $Z=1/3$. Simultaneously the coherent bandwidth is $ZW$: decreasing $Z$ does not supply an unlimited transition-temperature gain. The published argument explicitly allows deviations near the Mott boundary; its underlying DMFT model uses an infinite-coordination Bethe lattice. No self-consistent DMFT calculation or measured transition follows from this toy sweep.\n\nEvidence: theory. Sources: source-e2b9d469a7c556df.\n\nConditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.\n\nVerification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.\n\n### scwiki-d9-claim-experimental-criteria-1\n\nFor fcc Cs₃C₆₀, Ganin and colleagues report a pressure-dependent magnetic onset: 25.6 K at 1.3 kbar has only about 0.1% shielding, whereas 29.7 K at 2.2 kbar has about 12%. The maximum is approximately 35 K near 7 kbar, equivalent to 0.7 GPa. Measurements use 20 Oe, zero-field-cooled/field-cooled protocols and a tin pressure reference. A15 Cs₃C₆₀ reaches a separately reported maximum near 38 K; its value must not be assigned to the fcc sample.\n\nEvidence: experiment. Sources: source-634d02f3c2bfde0d, source-5e6d3e7ed715ad6a.\n\nConditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.\n\nVerification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.\n\n### scwiki-d9-claim-experimental-criteria-2\n\nThe fcc study also separates magnetic ordering near 2.2 K from the A15 ordering scale near 46 K. Neither is a superconducting transition. Multiphase powders and small shielding fractions require particular care when locating the first superconducting signal. The magnetometry pressure range ends near 10.6 kbar; the separate diffraction measurements extend to much higher pressures. Combining those ranges would falsely imply that superconductivity was measured throughout the structural experiment.\n\nEvidence: experiment. Sources: source-5e6d3e7ed715ad6a.\n\nConditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.\n\nVerification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.\n\n### scwiki-d9-claim-experimental-criteria-3\n\nPublished online on 9 June 2026, Shchukin and colleagues tune Rb uptake in nanostructured C₆₀ films. Figure 2f labels Rb₂.₇₁C₆₀ with $T_{\\mathrm{onset}}=22.4$ K and $T_{\\mathrm{zero}}=7.0$ K, and Rb₂.₉₈C₆₀ with 26.4 K and 14.5 K. The former criterion is a local resistivity maximum; the latter uses $d\\rho/dT<5\\times10^{-4}$ mΩ cm K⁻¹ in the plotted low-temperature window. It is a stated operational criterion, not an instrument-independent definition of exact zero resistance.\n\nEvidence: experiment. Sources: source-64cd48d99353501a.\n\nConditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.\n\nVerification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.\n\n### scwiki-d9-claim-experimental-criteria-4\n\nThat experiment uses Raman analysis with relative scattering cross sections to estimate composition, and van der Pauw transport. The 10 μA intercalation current differs from the 1 μA resistance-probe current. Stoichiometry, grain connectivity, thickness and transition criterion must accompany any comparison with bulk rubidium fullerides. The supplement and underlying transport datasets have not been independently reanalyzed here.\n\nEvidence: experiment. Sources: source-64cd48d99353501a.\n\nConditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.\n\nVerification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.\n\n### scwiki-d9-claim-limits-and-disputes-1\n\nMitrano's optical study and Budden's longer-lived driven response concern pumped K₃C₆₀. A finite-frequency inductive response and suppressed transient resistance constrain the nonequilibrium state, but do not by themselves establish an equilibrium thermodynamic transition. Budden's final Figure 4 separates two measurements at a 100 K base temperature and approximately 25 mJ cm⁻² pump fluence:\n\n| Measurement | What the reported value means |\n|---|---|\n| Optical, Fig. 4a; 200 ps pump | Zero-frequency resistivity extrapolated from a Drude–Lorentz fit to transient optical conductivity; error bars reflect the fit confidence interval. |\n| Electrical, Fig. 4b; 75 ps pump | Transient two-terminal resistance after contact correction from a separate static four-terminal measurement; the shaded band estimates calibration error. |\n\nThe electrical readout uses a 1 ns voltage probe pulse. The corrected resistance is compatible with zero within the stated calibration uncertainty, and recovers on a tens-of-nanoseconds timescale. This supports the authors' assignment of a metastable superconducting state; it does not turn the 100 K measurement condition into an equilibrium Tc. Neither the pump duration nor the probe duration is the state lifetime. Both records retain `transient-response` temperatures with no equilibrium Tc. Complete supplement review, raw-data refitting and comparison of alternative conductivity models remain open.\n\nEvidence: experiment. Sources: source-6ee3670220e24ff1, source-07be806c0002c690.\n\nSource relationship: mixed-source-and-local-derivation. Budden final Fig.4/caption and text supply distinct fit/calibration errors, 200ps and75ps pumps, 1ns voltage probe,100K base and transient recovery. Exclusion from equilibrium Tc rankings is an editorial classification; it does not claim an independent adjudication of the driven-state mechanism.\n\nConditions: Budden final Fig.4,100K base,approximately25mJ/cm2,200ps optical/75ps transport pumps; electrical1ns voltage probe; optical extrapolation and contact-corrected transient transport are distinct.\n\nVerification scope: Selected final published Fig.4/caption and p.615 text with figure pixels inspected; complete supplement and raw-data fits not checked.\n\n### scwiki-d9-claim-limits-and-disputes-2\n\nThe historical hole-doped C₆₀ claim at 52 K was retracted on 6 March 2003. The original paper and its notice are retained together for traceability; the withdrawn value is excluded from experimental transition records. The notice identifies concerns about device-measurement data following an independent investigation. A citation in an older, otherwise valid paper does not restore the withdrawn claim.\n\nEvidence: experiment. Sources: source-091fb85b144daad9, source-8822fee6435cf8cc.\n\nConditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.\n\nVerification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.\n\n### scwiki-d9-claim-discovery-implications-1\n\nFullerides motivate simultaneous control of bandwidth, local vibronic interactions, molecular valence and disorder. A superconducting dome near a Mott state is compatible with cooperation between phonons and correlations; it does not uniquely determine the pairing kernel. Neither a fully open gap nor proximity to a magnetic insulator proves that one interaction acts alone. Report model assumptions beside the experimental evidence used to constrain them.\n\nEvidence: experiment. Sources: source-5e6d3e7ed715ad6a, source-e2b9d469a7c556df.\n\nConditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.\n\nVerification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.\n\n### scwiki-d9-claim-discovery-implications-2\n\nCurrent-driven intercalation offers a method for tuning samples rather than a new bulk temperature record. Reproducible optimization needs composition maps, measurement-current controls and comparable transition definitions. Keep pressure polymorphs and optically driven states separate when selecting targets: their conditions cannot be collapsed into a single family-wide Tc ranking.\n\nEvidence: experiment. Sources: source-64cd48d99353501a, source-5e6d3e7ed715ad6a, source-07be806c0002c690.\n\nConditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.\n\nVerification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.\n\n## Revision and review\n\nArticle ID: scwiki-d9. Revision: 2da5142890f83dc4f172. Updated: 2026-10-20.\n\nReview scope: Selected fcc Cs3C60 pressure/magnetometry, fulleride model equations, 2026 intercalation transport criteria, prior scoped driven-state readings and complete indexed retraction notice. Publisher notice identifying the 24 February 2016 Mitrano caption correction checked separately on 19 October 2026. Follow-up ideal filling versus actual multiphase sample and selected final Budden Fig.4/text.\n\n- Full scientific acceptance, complete final-version comparisons and raw-data reproduction remain open.\n- 1991 discoveries remain abstract-level; 2008 A15 methods have not been reviewed.\n- The 2026 supplement and complete transient-state supplement and raw data remain outside this check.\n- No computed DMFT phase diagram, microscopic-mechanism uniqueness or device qualification is claimed.\n\nSource: [D_material_families/D9_fullerenes.md](https://github.com/JackZH26/jzis-superconductivity/blob/0a7c9d6696804ec26aa12f8eed68b55c9b3c0fcf/D_material_families/D9_fullerenes.md), commit 0a7c9d6696804ec26aa12f8eed68b55c9b3c0fcf, SHA-256 7fb6155c2847a4c14bfe3ba43e213f2ae8f83dfbe12019478fe94ca8d29cf392.\n","wordCount":1100}}