Strong and nearly 100% spin-polarized second-harmonic generation from ferrimagnet Mn2RuGa

Second-harmonic generation (SHG) has emerged as a promising tool for detecting electronic and magnetic structures in noncentrosymmetric materials, but $100%$ spin-polarized SHG has not been reported. In this work, we demonstrate nearly $100%$ spin-polarized SHG from the half-metallic ferrimagnet ${\mathrm{Mn}}_{2}\mathrm{RuGa}$. A band gap in the spin-down channel suppresses SHG, so the spin-up channel contributes nearly all the signal, as large as 3614 pm/V about ten times larger than that of GaAs. In the spin-up channel, ${\ensuremath{\chi}}_{xyz}^{(2)}$ is dominated by the large intraband current in three highly dispersed bands near the Fermi level. With the spin-orbit coupling, the reduced magnetic point group allows additional SHG components where the interband contribution is enhanced. Our finding is important as it predicts a large and complete spin-polarized SHG in an all-optical spin-switching ferrimagnet. This opens the door for future applications.