Interacting and higher-order topological spin excitations
Speaker: Alexander Mook (University of Basel, D. Loss group)
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Title: Interacting and higher-order topological spin excitations
Speaker: GHE Fellow A. Mook (University of Basel, D. Loss group)
Date: March 23rd 2021 @ 2pm
Place: Online zoom seminar
Condensed matter systems admit topological collective excitations above a trivial ground state, an example being Chern insulators formed by Dirac bosons with a gap at finite energies. However, in contrast to electrons, there is no particle-number conservation law for collective excitations. This gives rise to particle number nonconserving many-body interactions the influence of which on single-particle topology is an open issue of fundamental interest in the field of topological quantum materials.
Herein, I concentrate on magnons that are the elementary spin excitations of ferromagnets. A ferromagnet with Chern-insulating behavior of magnons exhibits a magnonic spectral gap hosting topologically protected chiral edge modes that unidirectionally revolve the sample. Since these chiral edge magnons may serve as directed information highways in next-generation technologies, a fundamental understanding of their formation and stability is at the very core of the topological magnonics paradigm.
I present topological magnons in three different setups: (i) skyrmion crystals, (ii) saturated chiral magnets, and (iii) stacks of honeycomb-lattice van der Waals magnets. These setups respectively serve as platforms to study (i) quantum damping due to spontaneous quasiparticle decay , (ii) interaction-stabilized topological gaps in the magnon spectrum , and (iii) second-order topology in three-dimensional samples that admit chiral states along their hinges, where facets intersect .
 Alexander Mook, Jelena Klinovaja, and Daniel Loss, Phys. Rev. Research 2, 033491 (2020)
 Alexander Mook, Kirill Plekhanov, Jelena Klinovaja, Daniel Loss, arXiv:2011.06543 (2020)
 Alexander Mook, Sebastián A. Díaz, Jelena Klinovaja, Daniel Loss, arXiv:2010.04142 (2020)