Proposal for all-electrical skyrmion detection in van der Waals tunnel junctions

TL;DR

This paper demonstrates the feasibility of all-electrical skyrmion detection in 2D van der Waals materials using advanced quantum transport calculations, revealing giant tunneling magnetoresistance effects in tunnel junctions.

Contribution

It introduces a novel approach for skyrmion detection in 2D vdW magnets via tunneling magnetoresistance, supported by first-principles quantum transport simulations.

Findings

Large TAMR observed around Fermi energy in vdW tunnel junctions.

Giant NCMR values for atomic-scale skyrmions due to spin-mixing.

Enhanced TAMR and NCMR in tunnel junctions compared to STM geometry.

Abstract

A major challenge for magnetic skyrmions in atomically thin van der Waals (vdW) materials is reliable skyrmion detection. Here, based on rigorous first-principles calculations, we show that all-electrical skyrmion detection is feasible in 2D vdW magnets via scanning tunneling microscopy (STM) and in planar tunnel junctions. We use the nonequilibrium Green's function method for quantum transport in planar junctions, including self-energy due to electrodes and working conditions, going beyond the standard Tersoff-Hamann approximation. We obtain a very large tunneling anisotropic magnetoresistance (TAMR) around the Fermi energy for a vdW tunnel junction based on graphite/Fe$_3$GeTe$_2$/germanene/graphite. For atomic-scale skyrmions the noncollinear magnetoresistance (NCMR) reaches giant values. We trace the origin of the NCMR to spin-mixing between spin-up and -down states of $p_z$ and $d_{z^2}$ character at the surface atoms. Both TAMR and NCMR are drastically enhanced in tunnel junctions with respect to STM geometry due to orbital symmetry matching at the interface.