Dynamics of Dirac strings and monopole-like excitations in chiral magnets under a current drive

TL;DR

This paper investigates the behavior of Dirac string-like monopoles in chiral magnets under electric currents, revealing their role in skyrmion line dynamics, phase transitions, and potential experimental detection methods.

Contribution

It provides a detailed analysis of monopole dynamics in chiral magnets, including creation, annihilation, and controlled manipulation under current drive, and predicts observable transport signatures.

Findings

Monopoles and antimonopoles drive skyrmion line creation and destruction.

High currents induce a chiral liquid phase with proliferated monopoles.

An inhomogeneous current can control monopole creation and induce measurable electric fields.

Abstract

Skyrmion lines in metallic chiral magnets carry an emergent magnetic field experienced by the conduction electrons. The inflow and outflow of this field across a closed surface is not necessarily equal, thus it allows for the existence of emergent monopoles. One example is a segment of skyrmion line inside a crystal, where a monopole and antimonopole pair is connected by the emergent magnetic flux line. This is a realization of Dirac string-like excitations. Here we study the dynamics of monopoles in chiral magnets under an electric current. We show that in the process of creation of skyrmion lines, skyrmion line segments are first created via the proliferation of monopoles and antimonopoles. Then these line segments join and span the whole system through the annihilation of monopoles. The skyrmion lines are destroyed via the proliferation of monopoles and antimonopoles at high currents, resulting in a chiral liquid phase. We also propose to create the monopoles in a controlled way by applying an inhomogenous current to a crystal. Remarkably, an electric field component in the magnetic field direction proportional to the current squared in the low current region is induced by the motion of distorted skyrmion lines, in addition to the Hall and longitudinal voltage. The existence of monopoles can be inferred from transport or imaging measurements.