Pseudo-gap at the Fermi level in K3C60 observed by photoemission and inverse photoemission

Photoemission and inverse photoemission spectroscopy has been used on C60 and K3C60 to study the change of the electronic structure upon alkali doping and its relation to the occurrence of superconductivity. The experimental results show that alkali doping does not lead to a rigid filling of the lowest unoccupied molecular-orbital band by the doped electrons but causes a transfer of electronic states from that band to an additional band produced in the band gap. A comparison of the photoemission and inverse photoemission spectra indicates that a pseudo-gap of about 0.5 eV opens at the Fermi level in K3C60. Possible origins for the pseudo-gap and its relation to superconductivity are discussed.