Wochenübersicht

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.

With the aim of contributing to the understanding of the motion of biological agents in porous media, we consider a minimal model fo active elongated particles and show that the motion of such active filaments in a porous medium depends critically on flexibility, activity and degree of polymerization. For given Peclet number, we observe a transition from localisation to diffusion as the stiffness of the chains is increased. Whereas stiff chains move almost unhindered through the porous medium, flexible ones spiral and get stuck. Their motion can be accounted for by the model of a continuous time random walk with a renewal process corresponding to unspiraling. The waiting time distribution is shown to develop heavy tails for decreasing stiffness, resulting in subdiffusive and ultimately caged behaviour.