Dissipative Antiferromagnetic Dynamics
Seters, Daan van
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No consensus exists on the equations that govern the dissipative dynamics of antiferromagnets. In particular, from phenomenological considerations (H. Y. Yuan, Liu, et al. 2019) one expects inter-sublattice damping terms in the sublattice dynamics. These terms are not present in the Landau-Lifshitz-Gilbert equations that are commonly used to describe individual sublattice dynamics. In this thesis, we present a Caldeira-Leggett approach within the Keldysh path integral formalism to base the dissipative equations for two-sublattice antiferromagnets on a more microscopic description. From this, we argue that the dissipative dynamics are determined by the specific form of system-bath structure through which the system dissipates. We recover phenomenological equations in the quasi-classical limit and find that the presence of inter-sublattice damping terms originate from the thermal coupling between the sublattices. Remarkably, we find that in a special case the N´eel order is a dissipation-free mode. Subsequently, we argue that the existence of dissipation-free modes is a more general phenomenon and will occur in systems composed of two subsystems where the bath is shared between the two subsystems.
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