Abstract
We predict the existence of Einstein-de Haas effect in topological magnon insulators. Temperature variation of angular momentum in the topological state shows a sign change behavior, akin to the low temperature thermal Hall conductance response. This manifests itself as a macroscopic mechanical rotation of the material hosting topological magnons. We show that an experimentally observable Einstein-de Haas effect can be measured in the square-octagon, the kagome, and the honeycomb lattices. Albeit, the effect is the strongest in the square-octagon lattice. We treat both the low and the high temperature phases using spin wave and Schwinger boson theory, respectively. We propose an experimental set up to detect our theoretical predictions. We suggest candidate square-octagon materials where our theory can be tested.
Highlights
The Einstein-de Haas (EdH) effect, predicted in 1908 by the Nobel Laureate Owen W
In the subsequent appendices we present the equations for spin-wave Hamiltonians for the honeycomb and the kagome lattices (Appendix A), the expressions for Schwinger boson mean field theory equations (Appendix B), the magnetic and topological phase diagrams (Appendix C), edge state geometry of a strip sample (Appendix D), thermal Hall conductance and angular momentum expressions (Appendix E), the nonequilibrium Green’s function (NEGF) equations (Appendix F), and the realistic materials parameters (Appendix G)
We have demonstrated the existence of the EdH effect in only these three lattices, our formalism, analysis approach, and eventual conclusions will hold for a wider variety of frustrated ferromagnetic systems
Summary
The Einstein-de Haas (EdH) effect, predicted in 1908 by the Nobel Laureate Owen W. In a quantum spin Hall state the bulk is insulating, whereas the edge can support helical transport modes These novel topological states are robust against external perturbation such as an external magnetic field. The thermal Hall effect has been found in various other magnetic systems such as spin liquids [19,20], multiferroics [21], antiferromagnets [22,23,24,25], and the pseudogap phase of a cuprate superconductor [26]. In the subsequent appendices we present the equations for spin-wave Hamiltonians for the honeycomb and the kagome lattices (Appendix A), the expressions for Schwinger boson mean field theory equations (Appendix B), the magnetic and topological phase diagrams (Appendix C), edge state geometry of a strip sample (Appendix D), thermal Hall conductance and angular momentum expressions (Appendix E), the NEGF equations (Appendix F), and the realistic materials parameters (Appendix G)
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