Shangjie Zhang Qualifying Exam

Abstract: With magnetic order and macroscopic polarization simultaneously present and coupled with each other, magnetoelectric multiferroics have drawn great research interest in the underlying physics, and their potential applications towards spintronic and next-generation memory devices. The emergence of Van der Waals materials further broadens the landscape of research on multiferroics, owing to the ease of tuning the physical properties and creating new phases with accessible methods like stacking and twisting. Here we demonstrate that using spectroscopic techniques, we can make a comprehensive characterization of the coupled equilibrium order parameters and collective excitations in multiferroics. Moreover, intense nonlinear optical drive can push the materials out of equilibrium, leading to hidden phases with exotic properties which are not available in equilibrium.