Competition between quantum spin tunneling and Kondo effect

David Jacob,Joaquin Fernández-Rossier

doi:10.1140/epjb/e2016-70402-2

Abstract

Quantum spin tunneling and Kondo effect are two very different quantum phenomena that produce the same effect on quantized spins, namely, the quenching of their magnetization. However, the nature of this quenching is very different so that quantum spin tunneling and Kondo effect compete with each other. Importantly, both quantum spin tunneling and Kondo effect produce very characteristic features in the spectral function that can be measured by means of single spin scanning tunneling spectroscopy and allows to probe the crossover from one regime to the other. We model this crossover, and the resulting changes in transport, using a non-perturbative treatment of a generalized Anderson model including magnetic anisotropy that leads to quantum spin tunneling. We predict that, at zero magnetic field, integer spins can feature a split-Kondo peak driven by quantum spin tunneling.

Highlights

Quantum spin tunneling (QST) and Kondo effect are two ubiquitous and widely studied [1,2,3] phenomena in the broad field of nanoscale magnetism
The resulting changes in transport, using a non-perturbative treatment of a generalized Anderson model including magnetic anisotropy that leads to quantum spin tunneling
The Kondo effect is most often associated with half-integer spins, but it has been observed in a variety of integer spin systems, such as quantum dots with an even number of electrons [7], various integer spin magnetic molecules [8,9,10] and molecular oxygen adsorbed on gold [11]

Summary

Introduction

Quantum spin tunneling (QST) and Kondo effect are two ubiquitous and widely studied [1,2,3] phenomena in the broad field of nanoscale magnetism. In this work we address how the competition between Kondo screening and QST affect the STM inelastic conductance and we predict a new physical phenomenon, the splitting of the Kondo peak at zero magnetic field due to quantum spin tunneling. Both the inelastic steps [21] and the Kondo features [22,23,24,25] can be described using a Kondo Hamiltonian where the atomic spin is described with a single-ion quantized spin interacting, via exchange, with the conduction electrons of the surface. Density functional theory (DFT) calculations show that often charge is not quantized in magnetic adatom systems [26,27]

Model and method

Results

Conclusions