Zhuquan Zhang

Massachusetts Institute of Technology

Understanding and controlling interactions between quasiparticles lie at the heart of condensed matter research. In magnetically ordered systems, collective spin precessions give rise to spin waves—whose quantized excitations are known as magnons. While there is growing interest in manipulating magnonic states far from thermal equilibrium, achieving and elucidating coherent couplings between distinct magnon modes remain longstanding challenges. In this talk, I will present our recent work on coherent nonlinear magnon-magnon interactions in canted antiferromagnets, driven by tailored terahertz fields. We demonstrate a unidirectional magnon upconversion process and identify correlated magnonic responses at both the sum and difference frequencies of the interacting modes. By tuning the difference-frequency generation to resonate with a low-frequency magnon, we achieve parametric amplification of magnon coherence. Moreover, by increasing the drive strength to push the system far from equilibrium, we reveal magnon self-interactions. These findings provide new insights into coherent magnon-magnon interactions in antiferromagnets and advance the frontiers of spintronics and magnonics into the ultrafast nonlinear regime.