Metallic picene/C60heterojunctions and the effect of potassium doping

Abstract

A metallic system without any further doping was obtained combining, in a bulk film, heterojunctions made by subsequent depositions of ${\mathrm{C}}_{60}$ and picene layers on Ag(111). This is caused by the formed dipole between the two molecules due to the huge difference in electron affinities and the charge transfer from the substrate. The above situation and the expected molecular geometry have also a role when the heterojunction film is doped with potassium. ${\mathrm{C}}_{60}$ phases diverse from those observed in bulk ${\mathrm{C}}_{60}$, especially, a metallic state with continuous alkali doping of the LUMO bands was found. This opens the way towards novel bulk molecular heterojunction structures that may create new electronic phases in strongly correlated molecular materials. The present case appears as the only manner known so far to form a bulk metallic ${\mathrm{K}}_{x}{\mathrm{C}}_{60}$ system ($0\phantom{\rule{0.16em}{0ex}}l\phantom{\rule{0.16em}{0ex}}x\phantom{\rule{0.16em}{0ex}}l\phantom{\rule{0.16em}{0ex}}6$) that may evoke the possibility of seeing the awaited dome-shaped region of the doping-temperature phase diagram if the system should show superconductivity.