Robin Neumann has successfully defended his PhD
“It has been an incredible privilege to be part of the International Max Planck Research School (IMPRS) and the Max Planck Graduate Center (MPGC). The support, guidance, and opportunities they offered have been instrumental in shaping both my research and my personal development during my PhD. I enjoyed the collaborative environment, the enriching workshops, and the sense of community they fostered.”
Title: “Theoretical Prediction for Probing Magnon Topology”
In this thesis, potential hallmarks of topological magnons in macroscopic observables of magnetic insulators are investigated. The magnon band structure for various models of two-dimensional ferromagnets, collinear and noncollinear antiferromagnets are characterized for their topological properties. The signatures of magnetic and topological phase transitions in the thermal Hall effect of magnons are analyzed in collinear antiferromagnets. On the basis of experimental data for the collinear antiferromagnet Na2Co2TeO6 the magnon transport theory is validated and extended to include magnon polarons. The extended theory explains important qualitative features of the transport measurements highlighting the importance of magnon polarons in the thermal Hall effect. Beyond the study of transport properties, the electric dipole moment of topological magnons is predicted, which causes an electric edge polarization in topological magnon insulators in equilibrium. Despite their charge neutrality, topological magnons are shown to respond to alternating electric fields rendering them electrically active. Those topological electromagnons are predicted to bring about unique footprints in the electrical absorption spectra at THz frequencies.
