Evidence for metallic states in potassium-intercalated picene film on graphite

We report the results of photoemission spectroscopy on the potassium concentration ($x$) dependence of K${}_{x}$ picene films on graphite. The results show a systematic shift of a whole valence band and the appearance of a clear Fermi edge for a certain value of $x$, with additional structures at higher binding energies. Observed spectral evolutions are reminiscent to those of doped C${}_{60}$, implying that the K${}_{x}$ picene film has multiple phases depending on the K concentration. Appearance of a clear Fermi edge, in contrast to multilayer K${}_{x}$ picene films on Au, SiO${}_{2}$, and Ag(111) substrates, where no clear Fermi edges are observed, suggests that the emergence of the metallic states for K${}_{x}$ picene films depends on the specific molecular orientations in the films on different substrates.