1. prethermal phases of matter: time-crystals, time quasi-crystals, and beyond

Wen Wei Ho

Stanford University, USA

28 January 2021 Thu 10 am

                                      IBS Center for Theoretical Physics of Complex Systems (PCS), Administrative Office (B349), Theory Wing, 3rd floor

                                      Expo-ro 55, Yuseong-gu, Daejeon, South Korea, 34126 Tel: +82-42-878-8633                     

Prethermalization refers to the physical phenomenon where a system evolves toward some long-lived non-equilibrium steady state before eventual thermalization sets in. In this talk, I will lay down a rigorous framework by which a many-body quantum system, driven periodically or quasi-periodically at high frequencies, exhibits prethermalization. I will explain how the prethermal state is governed by an effective Hamiltonian such that there is emergent energy conservation, and that the discrete time-translation symmetries of the drives are manifested as certain protected, emergent, on-site symmetries. These in turn underlie novel nonequilibrium interacting phases of matter like time crystals and time-quasicrystals, which spontaneously break the emergent symmetries. In the last part of the talk, I will explain how prethermalization can also arise not necessarily in the high-frequency driven limit. I will present scenarios where the prethermal state is characterized no longer by energy conservation, but instead only by emergent charge conservation. Nevertheless, prethermal phases of matter can still emerge under such settings.