Pseudo-gap at the Fermi level inK3C60observed by photoemission and inverse photoemission

Photoemission and inverse photoemission spectroscopy has been used on ${\mathrm{C}}_{60}$ and ${\mathrm{K}}_3$ ${\mathrm{C}}_{60}$ 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 ${\mathrm{K}}_3$ ${\mathrm{C}}_{60}$. Possible origins for the pseudo-gap and its relation to superconductivity are discussed.