Probing Kondo spin fluctuations with scanning tunneling microscopy and electron spin resonance

TL;DR

This paper proposes a theoretical framework combining ESR and STM to directly measure spin fluctuations in the Kondo effect, highlighting the sensitivity of the method to probe spins with magnetic anisotropy.

Contribution

It introduces a novel theoretical approach to analyze ESR-STM measurements of Kondo spin fluctuations using open quantum system techniques.

Findings

Sensitivity is highest for probe spins with transverse magnetic anisotropy.

The method can detect small level shifts caused by Kondo spin fluctuations.

The approach links ESR-STM signals to the dynamic spin susceptibility of the impurity.

Abstract

We theoretically analyze a state-of-the-art experimental method based on a combination of electron spin resonance and scanning tunneling microscopy (ESR-STM), to directly probe the spin fluctuations in the Kondo effect. The Kondo impurity is exchange coupled to the probe spin, and the ESR-STM setup detects the small level shifts in the probe spin induced by the spin fluctuations of the Kondo impurity. We use the open quantum system approach by regarding the probe spin as the "system" and the Kondo impurity spin as the fluctuating "bath" to evaluate the resonance line shifts in terms of the dynamic spin susceptibility of the Kondo impurity. We consider various common adatoms on surfaces as possible probe spins and estimate the corresponding level shifts. It is found that the sensitivity is most pronounced for the probe spins with transverse magnetic anisotropy.