Condensed-Matter Physics & Materials Science Seminar

Revealing the dynamics of collective excitations in strongly correlated electron systems 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, I will discuss the dynamics of collective excitations (e.g., excitons, magnons, phonons) from the perspective of ultrafast science [1-3]. In particular, I 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, I will describe our recent discovery of a transient antiferromagnetic metallic phase in a prototypical layered Mott insulator [4]. We observed this phase upon photoexciting a sub-Mott gap exciton-magnon mode, an exotic state of bound electron-hole pairs dressed with the spin degree of freedom [5]. Driving this peculiar exciton also allowed us to realize the coherent control of the underlying antiferromagnetic order for tens of picoseconds, a feature that can lead to the development of novel all-optical magnonic devices. [1] E. Baldini, Nonequilibrium Dynamics of Collective Excitations in Quantum Materials, Springer (2018) [2] E. Baldini*, C. A. Belvin* et al., Nat. Phys. 16, 541-545 (2020) [3] X. Li et al., Science 364, 1079-1082 (2019) [4] C. A. Belvin*, E. Baldini* et al., in review (2020) [5] S. Kang et al., Nature, in press (2020) https://bluejeans.com/956965585