Propagating energy modes in the heisenberg chain: Just plain magnons

Abstract

We show that the oscillations in the energy density observed in classical simulations on ferromagnetic chains are present in the antiferromagnet as well, and are not due to hydrodynamic “second magnon” modes, but arise from a singularity in the non interacting two spin wave density of states. Quantum occupation number effects change qualitatively the nature of the oscillations, producing a perfectly well defined mode at the spin wave frequency as T→0.