Generating high-order optical and spin harmonics from ferromagnetic monolayers

TL;DR

This paper demonstrates high-order harmonic generation in ferromagnetic monolayers, revealing spin-dependent signals and band structure information, thus opening new avenues in magneto-optical research and potential magnetic storage technologies.

Contribution

It introduces and experimentally demonstrates high-order harmonic generation in ferromagnetic monolayers, highlighting spin effects and relativistic influences previously unexplored in this context.

Findings

HHG in ferromagnetic monolayers carries spin information

HHG depends on relativistic spin-orbit coupling

Spin HHG appears only at even orders due to SU(2) symmetry

Abstract

High-order harmonic generation (HHG) in solids has entered a new phase of intensive research, with envisioned band-structure mapping on an ultrashort time scale. This partly benefits from a flurry of new HHG materials discovered, but so far has missed an important group. HHG in magnetic materials should have profound impact on future magnetic storage technology advances. Here we introduce and demonstrate HHG in ferromagnetic monolayers. We find that HHG carries spin information and sensitively depends on the relativistic spin-orbit coupling; and if they are dispersed into the crystal momentum ${\bf k}$ space, harmonics originating from real transitions can be ${\bf k}$-resolved and carry the band structure information. Geometrically, the HHG signal is sensitive to spatial orientations of monolayers. Different from the optical counterpart, the spin HHG, though probably weak, only appears at even orders, a consequence of SU(2) symmetry. Our findings open an unexplored frontier -- magneto-high-order harmonic generation.