SPECIAL SEMINAR: Probing hydrodynamics and thermalization in quantum spin systems

The presence of symmetries and conservation laws can have striking manifestations in the dynamic and thermalization behavior of interacting quantum systems. I will discuss two such manifestations arising in the context of ferromagnets driven out of equilibrium, and propose experiments to observe these behaviors. First, I will show that ferromagnets can enter the hydrodynamic regime when magnon density is sufficiently large. A key fingerprint of this regime is the existence of a sound mode which governs dynamics at small frequencies and is manifested as an excitation of the longitudinal spin component [1]. Such mode can be accessed with recently-introduced spin qubit magnetometers, which are ideally suited to probe dynamics in quantum spin systems [2,3]. Second, I will describe thermalization dynamics when ferromagnets are pumped into a highly non-thermal state. Despite being far from equilibrium, thermalization can nonetheless exhibit universal features, namely, universal scaling in time and momentum analogous to that arising in heavy ion collisions and in the early universe after inflation. Finally, I will address the effects of SU(2) symmetry on both hydrodynamics and thermalization in ferromagnets. 
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[1] JFRN, Podolsky, Demler, arXiv:1810.12333.
[2] JFRN, et al, Phys. Rev. B 98, 195433 (2018).
[3] Chatterjee, JFRN, Demler, arXiv:1810.04183.