Pumping approximately integrable systems.

Achim Rosch,

Univ. of Cologne

Weak perturbations can drive an interacting many-particle system far from its initial equilibrium state if one is able to pump into degrees of freedom approximately protected by conservation laws. This concept has for example been used to realize Bose-Einstein condensates of photons, magnons, and excitons. Integrable quantum system like the one-dimensional Heisenberg model are characterized by an infinite set of conservation laws. I will discuss a situation where integrability is only approximately realized and the system is driven away from thermal equilibrium by weak external pumping. More specifically, pumping can induce huge spin or heat currents since it activates local and quasi-local approximate conserved quantities. The resulting steady state is approximately, though efficiently, described by a generalized Gibbs ensemble, which depends sensitively on the structure of perturbations but not on their overall amplitude or on the initial state. We suggest to realize novel heat or spin pumps using spin-chain materials driven by THz radiation.