Low-Energy Scale Excitations in the Spectral Function of Organic Monolayer Systems

TL;DR

This paper reveals low-energy electronic excitations at the Fermi level in organic monolayer systems, showing their temperature dependence and potential connection to many-body effects like the Kondo phenomenon.

Contribution

It provides high-resolution spectroscopic evidence of low-energy excitations in organic monolayers and explores their possible origin in many-body interactions.

Findings

Observation of a sharp excitation feature at the Fermi level with ~25 meV width

Strong temperature dependence of the excitation feature

Potential link to Kondo-like many-body effects

Abstract

Using high-resolution photoemission spectroscopy we demonstrate that the electronic structure of several organic monolayer systems, in particular 1,4,5,8-naphthalene tetracarboxylic dianhydride and Copper-phtalocyanine on Ag(111), is characterized by a peculiar excitation feature right at the Fermi level. This feature displays a strong temperature dependence and is immediatly connected to the binding energy of the molecular states, determined by the coupling between the molecule and the substrate. At low temperatures, the line-width of this feature, appearing on top of the partly occupied lowest unoccupied molecular orbital of the free molecule, amounts to only $\approx 25$ meV, representing an unusually small energy scale for electronic excitations in these systems. We discuss possible origins, related e.g. to many-body excitations in the organic-metal adsorbate system, in particular a generalized Kondo scenario based on the single impurity Anderson model.