Spontaneous magnon decay is a generic feature of the magnetic excitations of anisotropic magnets and isotropic magnets with noncollinear order. After reviewing the properties of these excitations, I will argue that the effect of interactions on one-magnon states can, under many circumstances, be treated in terms of an effective, energy-independent, non-Hermitian Hamiltonian for the magnons. These types of non-Hermitian band structures have proven useful in describing the behaviour of a wide range of physical systems, such as those with gain or loss, and have provided a setting to explore new kinds of topology in condensed matter physics. I will argue that interacting magnons could provide a useful platform for realizing this kind non-Hermitian topology in the solid state. I will then show how this physics manifests in a concrete (and potentially experimentally relevant) model, and discuss signatures that may be observable in probes such as inelastic neutron scattering.

link to talk: https://mymedia.library.utoronto.ca/api/download/e698e199ac3f6e50094ebf14a64 fa984.mp4