Skyrmions and Electric Fields in Insulating Materials

Abstract

In insulating materials, conduction electrons and associated emergent fields are absent; instead, magnetic skyrmions in insulators induce spatially inhomogeneous charge distributions through the relativistic spin-orbit interaction. Depending on the symmetry of an underlying crystallographic lattice, skyrmions carry electric dipoles or quadrupoles and can be manipulated by an external electric field. This property may provide an energetically more efficient method to control skyrmions because the electric field in an insulating system causes only negligible Joule heat loss compared with the current-driven approach in a metallic system. In this chapter, this magnetoelectric nature of skyrmions is discussed. Skyrmions also show resonant oscillation against both ac magnetic and electric fields of gigahertz frequency. The interference of these excitations causes unique optical responses called directional dichroism, where the sign reversal of light (microwave) propagation direction gives different absorption spectra.