Theory of spin-polarized scanning tunneling microscopy applied to local spins

TL;DR

This paper develops a comprehensive theory for spin-polarized scanning tunneling microscopy, enabling detailed analysis of local spins, their interactions, and excitations through partitioned conductance contributions.

Contribution

It introduces a novel theoretical framework that decomposes tunneling conductance into background, dynamical, and noise-related parts, applicable to various magnetic configurations.

Findings

Partitioning of conductance allows extraction of total spin moment.

Dynamical conductance can generate high-frequency spin-dependent currents.

Analysis of spin excitations and exchange interactions is enhanced.

Abstract

We provide a theory for scanning tunneling microscopy and spectroscopy using a spin-polarized tip. It it shown that the tunneling conductance can be partitioned into three separate contributions, a background conductance which is independent of the local spin, a dynamical conductance which is proportional to the local spin moment, and a conductance which is proportional to the noise spectrum of the local spin interactions. The presented theory is applicable to setups with magnetic tip and substrate in non-collinear arrangement, as well as for non-magnetic situations. The partitioning of the tunneling current suggests a possibility to extract the total spin moment of the local spin from the dynamical conductance. The dynamical conductance suggests a possibility to generate very high frequency spin-dependent ac currents and/or voltages. We also propose a measurement of the dynamical conductance that can be used to determine the character of the effective exchange interaction between individual spins in clusters. The third contribution to the tunneling current is associated with the spin-spin correlations induced by the exchange interaction between the local spin moment and the tunneling electrons. We demonstrate how this term can be used in the analysis of spin excitations recorded in conductance measurements. Finally, we propose to use spin-polarized scanning tunneling microscopy for detailed studies of the spin excitation spectrum.