Shedding light on ferroic materials: novel phases of matter unraveled by ultrafast lasers

Ferroic materials such as ferroelectric, ferromagnetic, and ferroelastic materials exhibit a wealth of intriguing properties, which have provided a fertile ground for both fundamental research and a wide range of device applications. Symmetry plays a pivotal role in understanding ferroic orders. In light of symmetry classification, novel ferroic orders such as ferro-toroidal order and ferro-rotational order have been predicted and subsequently triggered tremendous interest in search of them. Second harmonic generation (SHG) is a process in which light frequency is doubled through its nonlinear interactions with a material. It provides a sensitive probe to the symmetry properties of ferroic materials. In this talk, I will first review the great success of SHG in studying ferroic materials. Then I will talk about the recent advance in this technique based on the rotational anisotropy experimental geometry. Finally, I will show that by exploiting our high-sensitivity rotational anisotropic SHG apparatus, we have recently identified the long-sought ferro-rotational order in a complex oxide RbFe(MoO4)2