Superconducting and normal state properties of the A3C60 compounds

Károly Holczer, Robert L. Whetten

Research output: Contribution to journalArticlepeer-review

60 Scopus citations

Abstract

This report is a critical review of the measurements and their interpretations of the normal and superconducting state of the A3C60 compounds, where A = alkali atom. These compounds are highly ionic [A+]3 · [C60]3- and form fcc lattices (cryolite structure) which locate the C60 icosahedra in sites of local cubic symmetry, thereby preserving the degeneracy of the tlu orbitals, allowing for the formation of a narrow half-filled band of a width comparable to or smaller than the different molecular excitation energies. The Tc -s of the more than a dozen compounds synthesized so far span the range 2-33 K; the variation of Tc with pressure and from material to material is assessed as an empirical Tc lattice parameter relation, suggestive that the attraction responsible for the Cooper pair formation is a local property of the C60 molecules and variations of the density of state ρ(ε{lunate}f) at the Fermi level (i.e., band width) determine Tc. The superconducting parameters, λL and ξ0 determined from critical field and μSR measurements, favoring a local pairing image, are marginally supportive of the expected density of state variations. The so far available 13C nuclear relaxation, susceptibility and ESR measurements in the normal state manifest several features more related to the complex correlated nature of the C60 molecules than free electron band effects of the simple lattice they are arranged in. The paper emphasizes these unusual characteristics.

Original languageEnglish (US)
Pages (from-to)1261-1276
Number of pages16
JournalCarbon
Volume30
Issue number8
DOIs
StatePublished - 1992
Externally publishedYes

Keywords

  • fullerene-alkali metal compounds
  • Fullerenes
  • metalation
  • superconductivity

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)

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