Electronic structure of K-doped picene film on HOPG

Abstract

We have performed potassium (K)-doping dependent photoemission (PES) measurements of picene film on highly oriented pyrolytic graphite (HOPG). K-doping dependent valence band PES data exhibits a shift of the valence band to a higher binding energy, indicative of the charge transfer from the K atoms to the picene film. K-doping dependent PES spectra near the Fermi level (E ) show the appearance and disappearance of a Fermi edge, indicating the metallic properties of the film at certain K concentrations. High-resolution PES spectrum at the lowest measured temperature does not show an opening of the superconducting gap, requesting further studies to explore the superconducting properties of the K-doped picene film. The results will be discussed by comparison with previous and recent spectroscopic studies.

Scanning Tunneling Microscopy Studies of Potassium-Doped Picene Films on Au(111) Surface

“…Recently, doping of metal atoms, especially alkali metal atoms, into polycyclic aromatic hydrocarbon (PAH) materials attracts much attention because of the appearance of superconductivity. ,− As a typical PAH molecule, picene has an armchair aromatic molecular configuration composed of five benzene rings. This molecule has been demonstrated to be superconducting upon potassium (K) or rubidium doping. ,− The superconducting transition temperature could be as high as 18 K. ,, However, because of the very low shielding fraction (<1.2%) and lack of repeatability, the superconductivity in such a system is questioned by Tanigaki and co-workers, Knupfer and co-workers, and Ruff et al Extensive efforts have been devoted to settle this debate. ,,,,,− ,,− Combining photoemission spectroscopy (PES) experiments and density functional theory plus dynamical mean-field theory (DFT+DMFT) calculation, Ruff et al found that K x Picene was a correlated Mott insulator for x = 1, 2, 3 . Yokoya and co-workers performed the PES studies on the electronic structure shift of K-doped picene film on highly oriented pyrolytic graphite (HOPG) .…”

“…This molecule has been demonstrated to be superconducting upon potassium (K) or rubidium doping. ,− The superconducting transition temperature could be as high as 18 K. ,, However, because of the very low shielding fraction (<1.2%) and lack of repeatability, the superconductivity in such a system is questioned by Tanigaki and co-workers, Knupfer and co-workers, and Ruff et al Extensive efforts have been devoted to settle this debate. ,,,,,− ,,− Combining photoemission spectroscopy (PES) experiments and density functional theory plus dynamical mean-field theory (DFT+DMFT) calculation, Ruff et al found that K x Picene was a correlated Mott insulator for x = 1, 2, 3 . Yokoya and co-workers performed the PES studies on the electronic structure shift of K-doped picene film on highly oriented pyrolytic graphite (HOPG) . Though the metallic behavior was revealed at a certain K-doping level, a superconducting gap was not observed at 4 K .…”

“…25 Yokoya and co-workers performed the PES studies on the electronic structure shift of K-doped picene film on highly oriented pyrolytic graphite (HOPG). 26 Though the metallic behavior was revealed at a certain K-doping level, a superconducting gap was not observed at 4 K. 26 Kelly et al claimed that the picene film on Ag(111) becomes amorphous after K doping. 20 Therefore, a detailed characterization of Kdoped picene at various doping ratios is essential to further clarify the debate.…”

Picene thin films on metal surfaces: Impact of molecular shape on interfacial coupling

“…Indeed, for picene monolayers on Au(111) a dimerization of the two molecules in the unit cell has been suggested . Another consequence of the zigzag shape of picene are the pseudo‐degenerated two lowest unoccupied molecular orbitals (LUMOs) and the likewise energetically closely spaced highest occupied molecular orbital (HOMO) and HOMO‐1, which is believed to be the key to the superconductivity with exceptionally high critical temperature of K‐doped picene . In order to show the impact of molecular shape and to correlate structure and electronic structure at organic‐metal interfaces, we measured low energy electron diffraction (LEED) and angle resolved ultraviolet photoelectron spectroscopy (ARUPS) of vacuum‐sublimed picene on Ag(111), Ag(110), Cu(111), and Cu(110) and compare our results with literature of pentacene on the same surfaces .…”