Scanning tunneling microscopy of adsorbed molecules on metalic surfaces for nearly localized atomic states

TL;DR

This paper models the electronic states of molecules adsorbed on metal surfaces using a Hubbard-Anderson framework, revealing conditions under which localized Kondo resonances dominate over molecular states, aligning with experimental STM data.

Contribution

It introduces a theoretical model for adsorbed molecules that captures the crossover between molecular states and localized Kondo resonances, matching experimental observations.

Findings

Identification of regimes where Kondo resonances dominate

Spectral density analysis matches STM measurements

Crossover behavior between molecular and localized states

Abstract

We consider a Hubbard-Anderson model which describes localized orbitals in five different sites hybridized both among themselves and with a continuum of extended states. A square planar geometry with an atom at the center is used to represent TBrPP-Co molecules. When the renormalized effective hopping between sites is small compared with a Kondo energy scale determined by the sitecontinuum hybridization, the system can be described as a set of independent Kondo resonances, rather than molecular states. We study the crossover between both regimes and analyze the spectral density of conduction electrons as a function of position. The results are in qualitative agreement with measurements of the differential conductance in a system with TBrPP-Co molecules adsorbed on a Cu(111) surface.