Theory of the different photoemission spectra of metallic and insulating C60 compounds

TL;DR

This paper explains the differences in photoemission spectra between metallic and insulating C60 compounds by analyzing electron-phonon coupling effects, showing that metallic screening influences spectral features.

Contribution

It introduces a theoretical model using the non-crossing approximation and moment expansion to accurately describe the spectral differences based on electron-phonon interactions.

Findings

Metallic K3C60 shows sharp Fermi edge and structure in PES.

Insulating K4C60 and K6C60 exhibit broad, structureless peaks.

Theoretical calculations match experimental PES data.

Abstract

Metallic K3C60 shows pronounced structure and a sharp Fermi edge in integrated photoemission spectra (PES) while the insulating K4C60 and K6C60 phases display only a broad structureless peak. We find that both types of spectra can be explained by the coupling to the optic vibrations of the K+/C60n- ionic lattice. This is suppressed in K3C60 due to metallic screening but is strong in the insulating phases. We use the non-crossing approximation to calculate the density of states (DOS) of electrons in K3C60 coupled to the intramolecular Hg modes in good agreement with the experiment. For K4C60 and K6C60 strong coupling to the low energy optic K+/C60n- modes controls the DOS and yields broad peaks in the PES. A moment expansion is used to calculate the position and width of these peaks which agree well with the experiment.