# Fulleride superconductors: Jahn–Teller coupling, Mott physics and driven states

Compare alkali-doped C60 compounds through pressure, molecular interactions and sample-specific transition criteria, with explicit boundaries for driven and retracted claims.

## Scope

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. [R5](#ref-source-e2b9d469a7c556df) [R4](#ref-source-5e6d3e7ed715ad6a) [R7](#ref-source-07be806c0002c690)

Nominal 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)

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. [R1](#ref-source-51b1a52d16139e58) [R2](#ref-source-0fb5ae1290bd2998)

## Mathematical assumptions

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. [R5](#ref-source-e2b9d469a7c556df)

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. [R5](#ref-source-e2b9d469a7c556df)

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. [R5](#ref-source-e2b9d469a7c556df)

## Experimental criteria

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. [R3](#ref-source-634d02f3c2bfde0d) [R4](#ref-source-5e6d3e7ed715ad6a)

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. [R4](#ref-source-5e6d3e7ed715ad6a)

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. [R8](#ref-source-64cd48d99353501a)

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. [R8](#ref-source-64cd48d99353501a)

## Limits and disputes

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:

| Measurement | What the reported value means |
|---|---|
| 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. |
| 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. |

The 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)

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. [R9](#ref-source-091fb85b144daad9) [R10](#ref-source-8822fee6435cf8cc)

## Discovery implications

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. [R4](#ref-source-5e6d3e7ed715ad6a) [R5](#ref-source-e2b9d469a7c556df)

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. [R8](#ref-source-64cd48d99353501a) [R4](#ref-source-5e6d3e7ed715ad6a) [R7](#ref-source-07be806c0002c690)

## Related topics

Continue 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).

## 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 |
|---|---|---|---|---|---|---|
| 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) |
| 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) |
| 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) |
| 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) |
| 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) |
| 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) |
| 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) |
| 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) |
| 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) |
| 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) |
| 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) |

## Sources

### Ref source-51b1a52d16139e58

[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.
### Ref source-0fb5ae1290bd2998

[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.
### Ref source-634d02f3c2bfde0d

[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.
### Ref source-5e6d3e7ed715ad6a

[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.
### Ref source-e2b9d469a7c556df

[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.
### Ref source-6ee3670220e24ff1

[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.
### Ref source-07be806c0002c690

[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.
### Ref source-64cd48d99353501a

[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.
### Ref source-091fb85b144daad9

[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.
### Ref source-8822fee6435cf8cc

[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.

## Claim evidence and conditions

### scwiki-d9-claim-scope-1

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.

Nominal 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.

Evidence: theory. Sources: source-e2b9d469a7c556df, source-5e6d3e7ed715ad6a, source-07be806c0002c690.

Source 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.

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.

Verification 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.

### scwiki-d9-claim-scope-2

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.

Evidence: experiment. Sources: source-51b1a52d16139e58, source-0fb5ae1290bd2998.

Conditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.

Verification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.

### scwiki-d9-claim-mathematical-assumptions-1

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.

Evidence: theory. Sources: source-e2b9d469a7c556df.

Conditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.

Verification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.

### scwiki-d9-claim-mathematical-assumptions-2

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.

Evidence: theory. Sources: source-e2b9d469a7c556df.

Conditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.

Verification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.

### scwiki-d9-claim-mathematical-assumptions-3

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.

Evidence: theory. Sources: source-e2b9d469a7c556df.

Conditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.

Verification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.

### scwiki-d9-claim-experimental-criteria-1

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.

Evidence: experiment. Sources: source-634d02f3c2bfde0d, source-5e6d3e7ed715ad6a.

Conditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.

Verification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.

### scwiki-d9-claim-experimental-criteria-2

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.

Evidence: experiment. Sources: source-5e6d3e7ed715ad6a.

Conditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.

Verification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.

### scwiki-d9-claim-experimental-criteria-3

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.

Evidence: experiment. Sources: source-64cd48d99353501a.

Conditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.

Verification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.

### scwiki-d9-claim-experimental-criteria-4

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.

Evidence: experiment. Sources: source-64cd48d99353501a.

Conditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.

Verification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.

### scwiki-d9-claim-limits-and-disputes-1

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:

| Measurement | What the reported value means |
|---|---|
| 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. |
| 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. |

The 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.

Evidence: experiment. Sources: source-6ee3670220e24ff1, source-07be806c0002c690.

Source 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.

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.

Verification scope: Selected final published Fig.4/caption and p.615 text with figure pixels inspected; complete supplement and raw-data fits not checked.

### scwiki-d9-claim-limits-and-disputes-2

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.

Evidence: experiment. Sources: source-091fb85b144daad9, source-8822fee6435cf8cc.

Conditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.

Verification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.

### scwiki-d9-claim-discovery-implications-1

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.

Evidence: experiment. Sources: source-5e6d3e7ed715ad6a, source-e2b9d469a7c556df.

Conditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.

Verification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.

### scwiki-d9-claim-discovery-implications-2

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.

Evidence: experiment. Sources: source-64cd48d99353501a, source-5e6d3e7ed715ad6a, source-07be806c0002c690.

Conditions: Stoichiometry, polymorph, pressure, probe and criterion are distinct; transient and magnetic temperatures are not equilibrium Tc.

Verification scope: Selected original passages, dated retraction notice and bounded model algebra; full scientific acceptance remains open.

## Revision and review

Article ID: scwiki-d9. Revision: 2da5142890f83dc4f172. Updated: 2026-10-20.

Review 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.

- 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.

Source: [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.