Past QuMat seminars in Utrecht

The QuMat seminars in Utrecht is a bi-weekly joint venture between Utrecht’s experimental and theoretical condensed matter physics groups.
Coming QuMat seminars are listed here.

Videos from previous talks are available on youtube and listed here.


Topological magnets support magnetic excitations with a topologically nontrivial spectrum. As a result, they exhibit chiral edge states akin to those known from the quantum Hall effect. These edge states are envisioned to facilitate backscattering-free information channels for magnetic signals [1]. Since spin excitations do not carry charge, they do not suffer from Joule heating and facilitate ultra-low energy computation. However, in contrast to electrons, there is no conservation law for spin excitations. This gives rise to particle number-nonconserving many-body interactions the influence of which on quasiparticle topology is an open issue of fundamental interest in the field of topological quantum materials. Herein, I concentrate on magnons – the elementary spin excitations of ferromagnets and antiferromagnets – and discuss several aspects of many-body effects caused by particle-number nonconservation. These include (i) quantum damping due to spontaneous quasiparticle decay [2], (ii) interaction-stabilized topological gaps and Dirac cones in the single-particle spectrum [3,4], and (iii) a topological hybridization of states belonging to different particle number sectors [5]. These effects highlight the fundamental difference between electronic and magnonic topology.

[1] Alexander Mook, Sebastián A. Díaz, Jelena Klinovaja, and Daniel Loss, “Chiral Hinge Magnons in Second-Order Topological Magnon Insulators,” Phys. Rev. B 104, 024406 (2021)

[2] Alexander Mook, Jelena Klinovaja, and Daniel Loss, “Quantum damping of skyrmion crystal eigenmodes due to spontaneous quasiparticle decay,” Phys. Rev. Research 2, 033491 (2020)

[3] Alexander Mook, Kirill Plekhanov, Jelena Klinovaja, and Daniel Loss, “Interaction-Stabilized Topological Magnon Insulator in Ferromagnets,” Phys. Rev. X 11, 021061 (2021)

[4] Matthias Gohlke, Alberto Corticelli, Roderich Moessner, Paul A. McClarty, Alexander Mook, “Spurious Symmetry Enhancement and Interaction-Induced Topology in Magnons,” arXiv:2211.15157 (2022)

[5] Alexander Mook, Rhea Hoyer, Jelena Klinovaja, and Daniel Loss, “Magnons, magnon bound pairs, and their hybrid spin-multipolar topology,” Phys. Rev. B 107, 064429 (2023), Editors’ Suggestion

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