Light-Matter-Coupling formalism for magnons: probing quantum geometry with light

arXiv (Cornell University)

Abstract

Nontrivial quantum geometry is a key feature of the wavefunctions of collective magnetic excitations in topological systems, but accessing it experimentally remains an open challenge. While Raman circular dichroism (RCD) has emerged as a promising probe, the fundamental link between the RCD and magnon quantum geometry has remained unsettled, and complicated by the fact that magnons are charge neutral. Here, we identify when and why this link exists. We show that, under broad conditions, the Fleury-Loudon Raman vertex can be obtained directly from a light-matter coupling expansion of the effective magnon Hamiltonian, bypassing the conventional microscopic derivation based on virtual electronic processes. This yields an analytical connection between the RCD and the Berry curvature of magnon bands. Applied to monolayer CrI\textsubscript{3}, our theory predicts finite temperature signatures of topological magnons in the RCD. These results establish a general route to quantum-geometry sensitive optical probes in magnonic systems.

Authors 4

1. Ying Shing Liu Aachen Institute for Theoretical Solid State Physics

   RWTH Aachen University

   Affiliation as printed

   Institute for Theoretical Solid State Physics, RWTH Aachen University, Aachen, Germany

2. Emil Viñas Boström

   Center for Free-Electron Laser Science · Max Planck Institute for the Structure and Dynamics of Matter

   Affiliation as printed

   Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, Hamburg, Germany

3. Michael A. Sentef

   University of Bremen · Center for Free-Electron Laser Science · Max Planck Institute for the Structure and Dynamics of Matter

   Affiliation as printed

   Institute for Theoretical Physics and Bremen Center for Computational Materials Science, University of Bremen, Bremen, Germany

   Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, Hamburg, Germany

4. Silvia Viola Kusminskiy Aachen Institute for Theoretical Solid State Physics

   Max Planck Institute for the Science of Light · RWTH Aachen University

   Affiliation as printed

   Institute for Theoretical Solid State Physics, RWTH Aachen University, Aachen, Germany

   Max Planck Institute for the Science of Light, Erlangen, Germany