Nonequilibrium Dynamics of Collective Excitations in Quantum Materials
Revealing the dynamics of collective excitations in quantum materials is a subject of pivotal importance, as collectivity lies at the origin of several cooperative phenomena that cause profound transformations, instabilities, and phase transitions. In this talk, Baldini will discuss the dynamics of collective excitations (e.g., excitons, magnons, phonons) from the perspective of ultrafast science. In particular, he will focus on the role that specific collective excitations play in the formation of hidden phases of matter, i.e. phases that do not have counterparts in the equilibrium phase diagrams of quantum materials. As an example, he will describe our recent discovery of a transient antiferromagnetic metallic phase in a prototypical van der Waals insulator. His team observed this phase upon photoexciting a spin-orbit-coupled exciton, an exotic state of bound electron-hole pairs dressed by the spin degree of freedom. Driving this peculiar exciton also allowed the team to realize the coherent manipulation of the underlying antiferromagnetic order for tens of picoseconds, a feature that can lead to the development of novel all-optical spintronic devices.