Sieberer, Lukas

Date:   Monday, December 9, 2019
Time:   15:00
Place:   ETH Zurich, Hönggerberg, HIT E 41.1
Host:    Oded Zilberberg

Order by anisotropy in two-dimensional driven-open systems

Lukas Sieberer
Institute for Quantum Optics and Quantum Information, Austria

The spatial and temporal order of two-dimensional systems with a continuous U(1) symmetry is determined by the dynamics of vortices. At low  temperatures, vortices of opposite charge form tightly bound pairs, while they are free to roam and destroy order as the temperature is increased. Interestingly, driving the system out of equilibrium alters the interaction of vortices in a drastic way: Instead of being long-ranged and thus capable of holding together pairs of vortices and anti-vortices in the ordered phase, out of equilibrium the interaction becomes screened, and defects proliferate. Here, we show that the structure of defects and their interaction can equally dramatically be modified by the breaking of rotational symmetry. For sufficiently strong spatial anisotropy, the force that binds pairs of defects can even be enhanced up to parametrically large scales. As a consequence, the vortex-unbinding crossover in such finite-size systems exhibits peculiar universal behavior. In the thermodynamic limit, we argue that the modified structure of defects renders a stable ordered phase possible. These results, which we obtain by analyzing the compact anisotropic Kardar-Parisi-Zhang equation, are relevant for a wide variety of physical systems, ranging from strongly coupled light-matter quantum systems such as exciton-polaritons, to recently proposed classical time crystals.