Strain-induced Anisotropic Terahertz Emission From a Fe(211)/Pt(110) Bilayer

Terahertz (THz) emission from a $\mathrm{Fe}(211)/\mathrm{Pt}(110)$ bilayer grown on $\mathrm{Mg}\mathrm{O}(110)$ is systematically investigated. The intensity of the emitted THz wave strongly depends on the magnetization (M) orientation, and the measured THz field is 11% larger for M||$\mathrm{Pt}[1\overline{1}0]$ than for M||Pt[001]. Using first-principles calculations combined with the superdiffusive spin-transport model, we reveal that the lattice distortion induced by epitaxial strain causes anisotropic behavior of the electronic conductance and spin Hall conductivity, which eventually lead to the aforementioned experimental observations. Our studies thus provide a route to modify THz emission utilizing the intrinsic crystal-structure degree of freedom.