La@C-60: A metallic endohedral fullerene

We have produced an endohedrally doped fullerene that shows a metal-like de nsity of states at the Fermi level. Individual La@C-60 clusters deposited o nto graphite exhibit a zero band gap as observed by scanning tunneling spec troscopy on single clusters at room temperature. Moreover, we find that an isolated La@C-60 cluster on graphite shows a reversible opening of a band g ap at a transition temperature of similar to 28 K. The transition is associ ated with a freezing of the vibrational motion of the La atom inside the fu llerene cage. The metallic behavior of La@C-60 is attributed to the presenc e of a dynamical dipole in the single cluster. (C) 2001 American Institute of Physics.