Jeffrey Rau

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Recently, magnon excitations have been explored as a potential route to
realizing analogues of the topological band structures that have become
ubiquitous in electronic systems. However, magnons are not necessarily
stable quasi-particles, with spontaneous magnon decay a generic feature
of anisotropic magnets or magnets with non-colinear order. In this talk
I will discuss two aspects of this physics: First, I will discuss how
sharp topological magnon bands can exist in spite of the presence
allowed decays, as realized in a Kitaev model in a large magnetic field.
Second, I will discuss an alternative scenario where decay in fact
drives the appearance new kinds of intrinsically non-Hermitian
topological physics. This can lead to new kinds of spectral features,
such as exceptional points and bulk "arcs" connecting them. I will
illustrate this physics through a concrete example: a honeycomb
ferromagnet with Dzyaloshinskii-Moriya exchange, comparing interacting
spin-wave calculations with an effective non-Hermitian model. Finally, I
discuss more broadly how the zoo of known topological protected magnon
band structures may serve as a nearly ideal platform for realizing
non-Hermitian physics in solid-state systems.

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MPI-PKS Dresden
Seminar Room of the Institute of Physics II
Contact: Ciarán Hickey