VIBRATIONAL SPECTROSCOPY OF SUPERCONDUCTING K3C60 BY INELASTIC NEUTRON-SCATTERING

INTERCALATION of C60 (buckminsterfullerene 1,2) by alkali metals 3 leads to superconducting compounds of stoichiometry A3C60 (refs 4-6) with transition temperatures T(c) as high as 33 K (ref. 7). These transition temperatures are considerably higher than those for alkali-metal-intercalated graphite (< 0.6 K) 8 and scale with the size of the face-centred-cubic unit cell 9. Here we present the results of an inelastic neutron scattering study of the vibrational spectrum of the superconducting fulleride K3C60 (T(c) = 19.3 K). We find significant changes in the peak positions and intensities principally of the intramolecular H(g) vibrational modes, both in the high-energy tangential (130-200 meV) and the low-energy radial (approximately 50 meV) regions, compared with the vibrational spectrum of C60 (refs 10, 11). Our results provide strong evidence for the importance of these modes in the pairing mechanism for superconductivity.