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 Kₓ 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 C₆₀, implying that the Kₓ picene film has multiple phases depending on the K concentration. Appearance of a clear Fermi edge, in contrast to multilayer Kₓ picene films on Au, SiO₂, and Ag(111) substrates, where no clear Fermi edges are observed, suggests that the emergence of the metallic states for Kₓ picene films depends on the specific molecular orientations in the films on different substrates.