NonHermitian topology of spontaneous magnon decay
Abstract
Spontaneous magnon decay is a generic feature of the magnetic excitations of anisotropic magnets and isotropic magnets with noncollinear order. In this Rapid Communication, we argue that the effect of interactions on onemagnon states can, under many circumstances, be treated in terms of an effective, energyindependent, nonHermitian Hamiltonian for the magnons. In the vicinity of Dirac or Weyl touching points, we show that the spectral function has a characteristic anisotropy arising from topologically protected exceptional points or lines in the nonHermitian spectrum. Such features can, in principle, be detected using inelastic neutron scattering or other spectroscopic probes. We illustrate this physics through a concrete example: a honeycomb ferromagnet with DzyaloshinskiiMoriya exchange. We perform interacting spinwave calculations of the structure factor and spectral function of this model, showing good agreement with results from a simple effective nonHermitian model for the splitting of the Dirac point. Finally, we argue that the zoo of known topological protected magnon band structures may serve as a nearly ideal platform for realizing and exploring nonHermitian physics in solidstate systems.
 Publication:

Physical Review B
 Pub Date:
 September 2019
 DOI:
 10.1103/PhysRevB.100.100405
 arXiv:
 arXiv:1904.02160
 Bibcode:
 2019PhRvB.100j0405M
 Keywords:

 Condensed Matter  Strongly Correlated Electrons
 EPrint:
 4+epsilon pages