SKM 2021 – scientific programme

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MA: Fachverband Magnetismus

MA 9: INNOMAG e.V. Diploma/Master Prize (2021)

MA 9.1: Talk

Wednesday, September 29, 2021, 12:30–12:50, H2

Orbital Magnetic Moment of Magnons — •Robin R. Neumann¹, Alexander Mook^1,2, Jürgen Henk¹, and Ingrid Mertig¹ — ¹Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, Halle (Saale), Germany — ²Department of Physics, University of Basel, Basel, Switzerland

It is commonly accepted that magnons—collective excitations in a magnetically ordered system—carry a spin of 1ℏ or, phrased differently, a magnetic moment of g µ_B. In this talk, I demonstrate that magnons carry magnetic moment beyond their spin magnetic moment. Our rigorous quantum theory uncovers a magnonic orbital magnetic moment brought about by spin-orbit coupling. We apply our theory to two paradigmatic systems where the notion of orbital moments manifests itself in novel fundamental physics rather than just quantitative differences. In a coplanar antiferromagnet on the two-dimensional kagome lattice the orbital magnetic moment gives rise to an orbital magnetization. While the spin magnetization is oriented in the kagome plane, the orbital magnetization also has a finite out-of-plane component leading to ‘orbital weak ferromagnetism.’ The insulating collinear pyrochlore ferromagnet Lu₂V₂O₇ exhibits a ‘magnonic orbital Nernst effects,’ i. e. transversal currents of orbital magnetic moment induced by a temperature gradient. The orbital magnetization and the orbital Nernst effect in magnetic insulators are two signatures of the orbital magnetic moment of magnons.