Emergent electrodynamics of skyrmions in a chiral magnet

TL;DR

This paper experimentally confirms the emergent electrodynamics of skyrmions in chiral magnets, demonstrating their quantized magnetic flux, induced electric fields, and low-current depinning, advancing understanding for potential applications.

Contribution

It provides quantitative experimental evidence for the emergent electrodynamics of skyrmions, including their quantized flux and low-current depinning in chiral magnets.

Findings

Quantitative Hall effect measurements confirm emergent electrodynamics.

Skyrmions depin from impurities at ultra-low current densities (~10^6 A/m^2).

Demonstrates connection between emergent and real electrodynamics in skyrmions.

Abstract

When an electron moves in a smoothly varying non-collinear magnetic structure, its spin-orientation adapts constantly, thereby inducing forces that act on both the magnetic structure and the electron. These forces may be described by electric and magnetic fields of an emergent electrodynamics. The topologically quantized winding number of so-called skyrmions, i.e., certain magnetic whirls, discovered recently in chiral magnets are theoretically predicted to induce exactly one quantum of emergent magnetic flux per skyrmion. A moving skyrmion is therefore expected to induce an emergent electric field following Faraday's law of induction, which inherits this topological quantization. Here we report Hall effect measurements, which establish quantitatively the predicted emergent electrodynamics. This allows to obtain quantitative evidence of the depinning of skyrmions from impurities at ultra-low current densities of only 10^6 A/m^2 and their subsequent motion. The combination of exceptionally small current densities and simple transport measurements offers fundamental insights into the connection between emergent and real electrodynamics of skyrmions in chiral magnets, and promises to be important for applications in the long-term.