Antiferromagnetic insulators with strong spin-orbit coupling, such as Sr2IrO4, present exciting platform for terahertz magnonics due to their ultrafast spin dynamics and sensitivity to external stimuli [1]. However, achieving precise control of magnon propagation remains challenging. In this talk, I will present Sr2IrO4, a quasi-two-dimensional antiferromagnetic Mott insulator with Jeff = 1/2 pseudospins, whose terahertz spin waves respond strongly to adjacent materials. Using resonant inelastic x-ray scattering, we systematically probed the spin-wave dispersion of Sr2IrO4 thin films interfaced with metallic and insulating crystals including 4d ruthenates. Our results reveal a notable softening of single-magnon modes near the (π/2, π/2) zone boundary in films adjacent to metallic crystals, while the magnon spectrum remains unchanged for insulating interfaces. Complementary Raman spectroscopy highlights a softening of two-magnon excitations and a hardening of phonon modes near metallic interfaces, pointing to electron-phonon interactions as the primary mechanism [2]. These findings suggest a novel means to control terahertz magnon propagation, distinct from conventional interfacial effects such as strain or doping. It also underscores the need for further theoretical studies to better understand the underlying microscopic interactions between magnons and phonons.
[1] H.-H. Kim et al. Nat. Commun. 13, 6674 (2022).
[2] S. Shrestha et al., Nat. Commun. 16, 3592 (2025).
This work was supported by National Science Foundation Grant No. DMR-2104296.