Simulation of inelastic spin flip excitations and Kondo effect in STM spectroscopy of magnetic molecules on metal substrates

TL;DR

This paper introduces a semi ab initio method combining density functional theory and many-body techniques to simulate inelastic spin flip excitations and Kondo effects in STM spectra of magnetic molecules on metal substrates, aligning well with experiments.

Contribution

It presents a novel computational scheme to accurately predict STM spectral features of magnetic molecules, incorporating magnetic anisotropy and many-body effects.

Findings

Good agreement with experimental spectra for Fe porphyrin molecules.

Reproduces spin flip excitation steps at finite bias.

Less accurate modeling of Kondo effect due to quantum interference neglect.

Abstract

Single-ion magnetic anisotropy in molecular magnets leads to spin flip excitations that can be measured by inelastic scanning tunneling microscope (STM) spectroscopy. Here I present a semi ab initio scheme to compute the spectral features associated with inelastic spin flip excitations and Kondo effect of single molecular magnets. To this end density functional theory calculations of the molecule on the substrate are combined with more sophisticated many-body techniques for solving the Anderson impurity problem of the spin-carrying orbitals of the magnetic molecule coupled to the rest of the system, containing a phenomenological magnetic anisotropy term. For calculating the STM spectra an exact expression for the dI/dV in the ideal STM limit, when the coupling to the STM tip becomes negligibly small, is derived. In this limit the dI/dV is simply related to the spectral function of the molecule-substrate system. For the case of an Fe porphyrin molecule on the Au(111) substrate, the calculated STM spectra are in good agreement with recently measured STM spectra, showing the typical step features at finite bias associated with spin flip excitation of a spin-1 quantum magnet. For the case of Kondo effect in Mn porphyrin on Au(111), the agreement with the experimental spectra is not as good due to the neglect of quantum interference in the tunneling.