HIGH-SENSITIVITY OF THE POSITRON-DENSITY DISTRIBUTION TO THE K-DOPING IN C-60

Distinct positron lifetimes in C60 and in K3C60 superconductors are observed: a single lifetime (375 ps) in pure C60 and two lifetimes (265 and 425 ps) in K3C60. The positron densities, computed by using the self-consistent orthogonalized linear combination of the atomic-orbital band structure in KxC60 (x = 0, 1, 2, 3, and 6) are presented. The strong dependence of the positron-density distribution on the amount of K doping, varying from interstitial sites outside the ball to the cavity inside the ball, demonstrates the use of the positron to probe local charge densities in C60-based superconductors.