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.

• Received 14 November 1991

DOI:https://doi.org/10.1103/PhysRevLett.68.1232