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Absence of a metallic phase at high pressures in C60

Naturevolume 354pages289291 (1991) | Download Citation



THE bonding between molecules in bulk solid C60 is extremely weak, making it a narrow-band semiconductor with an energy gap of 1.5 eV (ref. 1) for the face-centred cubic phase. Doping with alkali metals produces a metallic state which can be superconducting at temperatures as high as 33 K (ref. 2). The intermolecular coupling should have an important influence on the conductivity of the pure, semiconducting state: stronger coupling might induce a transition to a metallic or possibly even superconducting state, as is the case for silicon3, or it may result in a covalent solid such as diamond4. We have explored these possibilities by measuring the electrical resistivity of solid granular C60 up to pressures of 25 GPa. Our results show that the magnitude of the gap and the resistivity decrease with increasing pressures as the sample volume5 decreases. But eventual gap closure to give a metallic state is not observed; instead, there is a sudden transition at 15–20 GPa to a more insulating phase, possibly with covalent intermolecular bonding.

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  1. Centre de Recherches sur les Très Basses Temperatures, CNRS, BP 166X, Cedex 9, 38042, Grenoble, France

    • M. NÚñez Regueiro
    •  & P. Monceau
  2. Laboratoire d'Activation Moléculaire, Ecole Normale Supérieure, 24 Rue Lhomond, 75231, Paris, France

    • A. Rassat
  3. Groupe de Dynamique des Phases Condensées, Université de Montpellier, 34060, Montpellier, France

    • P. Bernier
    •  & A. Zahab
  4. On leave of absence from Centre Atomico Bariloche, 8400, Bariloche, Argentina

    • M. NÚñez Regueiro


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