Non-equilibrium phase transitions from time-dependent spin-wave theory
Jamir Marino (Harward University, Cambridge MA, USA)

This talk is a journey into non-equilibrium phases of interacting quantum spin chains resulting from quantum quenches or periodic drives. The common ground of our study is a version of Holstein-Primakoff expansion suited to strongly non-equilibrium conditions resulting in a self-consistent theory of spin waves coupled to a dynamical order parameter. We will present three examples: emergent chaotic dynamical ferromagnets in Ising chains with competing short and long range interactions; dynamical stabilisation of an analog of the many-body Kapitza pendulum in long-range interacting spin chains; and finally we will briefly discuss the onset of time crystals in spins collectively coupled to photons.