CMT Seminar with Liuyan Zhao: Probing multipolar orders in quantum materials using nonlinear optics

At the macroscopic scale, complex arrangements of electric and magnetic dipole moments call for multipole moments to describe. Such multipole moments can be present at the microscopic scale, such as within atomic lattice unit cells, and in fact, their collective organizations, multipolar orders, are proposed to explain many puzzling phenomena in a variety of quantum materials. However, their experimental detections are extremely challenging because of the lack of direct coupling fields to the tensorial multipolar order parameters. In this presentation, I will show our recent efforts in developing nonlinear optical spectroscopy to probe such multipolar orders, using two specific examples. The first is the ferro-rotational order which features the head-to-tail loop arrangements of electric dipoles. The second is the noncollinear antiferromagnetic order in a Kagome lattice. We will show how the multiple copies of electromagnetic fields combine together in nonlinear optics to couple to the tensorial multipolar order parameters and systematically track the symmetry evolution upon their emergence.