George E. Valley Jr. Prize Talk: Prethermal phases of matter in long-range interacting and classical many-body systems

Recent advances suggest that physical systems, which are taken out of equilibrium, can exhibit phenomena fundamentally richer than their static counterparts. For example, certain phases of matter that are provably forbidden in equilibrium, such as discrete time crystals, have found new life in periodically driven, non-equilibrium systems. In this talk, I will define the essential features of time crystalline order and describe two new venues where such order can be observed: 1) in a 1D disorder-free, long-range interacting system and 2) in a classical spin system. In both cases, the underlying workhorse is Floquet prethermalization - a phenomena which occurs in the high frequency limit of periodically driven many-body systems; in particular, when the drive frequency is large compared with the local energy scales of the system, there can exist a long-lived quasi-steady state - a so-called "prethermal" state - in which ordered phases of matter can remain stable for exponentially long time scales.