High harmonic generation in altermagnets

We study high harmonic generation in altermagnetic metals with and without spin-orbit coupling. The altermagnetism manifests itself in the magnetic field dependence of the low harmonics associated with intra-band dynamics. Spin-orbit coupling leads to additional higher energy peaks and plateau structures originating from inter-band transitions. While the pure altermagnet or spin-orbit system exhibits no circular dichroism in the high-harmonic response, an altermagnetic system with spin-orbit coupling shows such a dichroism. We also analyze the spin currents and their high harmonic spectrum.