Tunable Space-Time Crystal In Room-Temperature Magnetodielectrics

We report the experimental realization of a space-time crystal with tunable periodicity in time and space in a magnon Bose-Einstein condensate (BEC), formed in a room-temperature yttrium iron garnet (YIG) film by a microwave space-homogeneous magnetic field. The magnon BEC is prepared to have a well-defined frequency and nonzero wave vector. We demonstrate how the crystalline "density" as well as the time and space textures of the resulting crystal may be tuned by varying the experimental parameters: External static magnetic field, temperature, thickness of the YIG film, and power of the microwave field. The proposed space-time crystals provide an additional dimension for exploring dynamical phases of matter and can serve as a model nonlinear Floquet system, that brings in touch the rich fields of classical nonlinear waves, magnonics, and periodically driven systems.