Absence of photoemission from the Fermi level in potassium intercalated picene and coronene films: structure, polaron or correlation physics?

TL;DR

This study investigates the electronic structure of potassium-intercalated picene and coronene films, revealing no Fermi level emission and suggesting complex underlying physics beyond simple metallic behavior.

Contribution

It provides new insights into the electronic states of alkali-metal intercalated molecular films, challenging assumptions about their metallicity and superconductivity.

Findings

No Fermi level emission observed in intercalated films

Charge transfer occurs but does not lead to metallic states

Discussion of possible reasons for absence of metallicity

Abstract

The electronic structure of potassium intercalated picene and coronene films has been studied using photoemission spectroscopy. Picene has additionally been intercalated using sodium. Upon alkali metal addition core level as well as valence band photoemission data signal a filling of previously unoccupied states of the two molecular materials due to charge transfer from potassium. In contrast to the observation of superconductivity in K_xpicene and K_xcoronene (x ~ 3), none of the films studied shows emission from the Fermi level, i.e. we find no indication for a metallic ground state. Several reasons for this observation are discussed.