High-resolution combined tunneling electron charge and spin transport theory of N\'eel and Bloch skyrmions

TL;DR

This paper develops a combined charge and spin transport theory to analyze high-resolution tunneling electron imaging of Neel and Bloch skyrmions, revealing how their magnetic textures influence spin transport and can be identified via SP-STM.

Contribution

It introduces a novel combined charge and vector spin transport model for imaging and analyzing Neel and Bloch skyrmions with SP-STM, including effects of local chirality on apparent size.

Findings

SP-STM images can determine skyrmion helicity.

Spin transport vector components relate to charge current images.

Local chirality affects apparent skyrmion size.

Abstract

Based on a combined charge and vector spin transport theory capable of imaging noncollinear magnetic textures on surfaces with spin-polarized scanning tunneling microscopy (SP-STM), the high-resolution tunneling electron charge and coupled spin transport properties of a variety of N\'eel- and Bloch-type skyrmions are investigated. Axially symmetric skyrmions are considered within the same topology class characterized by a vorticity value of $m=1$, and their helicities are varied by taking $\gamma=0$ and $\pi$ values for the N\'eel skyrmions and $\gamma=-\pi/2$ and $\pi/2$ values for the Bloch skyrmions. Depending on the orientation of the magnetization of the STM tip as well as on the helicity and the time-reversal of the skyrmionic spin structures, several relationships between their spin transport vector components, the in-plane and out-of-plane spin transfer torque and the longitudinal spin current, are identified. The magnitudes of the spin transport vector quantities show close relation to standard charge current SP-STM images. It is also demonstrated that the SP-STM images can be used to determine the helicity of the skyrmions. Moreover, the modified spin polarization vectors of the conduction electrons due to the local chirality of the complex spin texture are incorporated into the tunneling model. It is found that this effect modifies the apparent size of the skyrmions. These results contribute to the proper identification of topological surface magnetic objects imaged by SP-STM, and deliver important parameters for current-induced spin dynamics.