Two-stage three-channel Kondo physics for an FePc molecule on the Au(111) surface

TL;DR

This paper models the complex Kondo physics of an FePc molecule on Au(111) using a two-stage impurity Anderson model, successfully explaining experimental STS spectra and revealing interference effects between multiple orbital channels.

Contribution

It introduces a detailed two-stage three-channel Kondo model for FePc on Au(111) and demonstrates its effectiveness in reproducing experimental spectra and understanding Kondo temperature scales.

Findings

The model accurately reproduces STS spectra between -60 mV and 20 mV.

Two distinct Kondo temperature scales are identified, T_K^z and T_K^π.

Interference between channels significantly reduces the lowest Kondo temperature.

Abstract

We study an impurity Anderson model to describe an iron phthalocyanine (FePc) molecule on Au(111), motivated by previous results of scanning tunneling spectroscopy (STS) and theoretical studies. The model hybridizes a spin doublet consisting in one hole at the $3d_{z^2}$ orbital of iron and two degenerate doublets corresponding to one hole either in the $3d_{xz}$ or in the $3d_{yz}$ orbital (called $\pi$ orbitals) with two degenerate Hund-rule triplets with one hole in the $3d_{z}$ orbital and another one in a $\pi$ orbital. We solve the model using a slave-boson mean-field approximation (SBMFA). For reasonable parameters we can describe very well the observed STS spectrum between sample bias -60 mV to 20 mV. For these parameters the Kondo stage takes place in two stages, with different energy scales $T_K^z > T_K^\pi$ corresponding to the Kondo temperatures related with the hopping of the $z^2$ and $\pi$ orbitals respectively. There is a strong interference between the different channels and the Kondo temperatures, particularly the lowest one is strongly reduced compared with the value in the absence of the competing channel.