Theory of Inelastic Electron Tunneling from a Localized Spin in the Impulsive Approximation

TL;DR

This paper derives a simple theoretical expression for conductance steps observed in inelastic electron tunneling from a single magnetic atom's spin, linking the conductance features to spin wave functions and exchange coupling.

Contribution

It introduces a straightforward model for inelastic tunneling conductance steps based on an impulsive approximation and spin matrix elements, clarifying previous experimental observations.

Findings

Derived a simple expression for conductance steps in inelastic tunneling.

Linked conductance step magnitudes to spin-polarized wave functions.

Validated the model against experimental data from magnetic adatoms.

Abstract

A simple expression for the conductance steps in the inelastic electron tunneling from spin excitations in a single magnetic atom adsorbed on a non-magnetic metal surfaces is derived. The inelastic coupling between the tunneling electron and the spin is via the exchange coupling and is treated in an impulsive approximation using the Tersoff-Hamann approximation for the tunneling between the tip and the sample. Our results for conductance steps justify the analysis carried out by Hirjebedin et al. [Science 317, 1199 (2007)] of observed step-like conductances by inelastic electron tunneling from spin excitations in a single magnetic adatom using a simple spin matrix element. In addition, our result gives a simple expression for the magnitudes of conductance steps and their lateral spatial variation with respect to the tip position, which can be calculated directly from spin-polarized wave functions at the Fermi level of the sample.