Chiral phonons for spintronics

Ulrich Nowak, University of Konstanz

The discovery and investigation of chiral phonons uncovered a variety of novel physical effects which are related to the chiral phonon's angular momentum as well as its associated magnetic field. Their interaction with the electron spin offers opportunities for an exploitation in spintronics, where they can be functionalized as additional carriers for the transport of anular momentum. However, the microscopic understanding of the coupled dynamics of the electronic angular momenta and the lattice degrees of freedom [1] is still incomplete.

This new research field calls for new modelling approaches and numerical tools. In this talk we report on recent developments in the microscopic understanding of the coupling between spin and lattice degrees of freedom with an emphasis on the exchange of angular momentum between these two subsystems. Specifically, we discuss a framework for spin-molecular dynamics that connects, on the one hand, to ab initio calculations of spin-lattice coupling parameters [2,3] and, on the other hand, to the magneto-elastic continuum theory. This framework allows for multi-scale modeling approaches including the development of material-specific atomistic models for the coupled spin and lattice degrees of freedom, the calculation and investigation of magnon-phonon dispersion relations [4], and the development and use of modelling tools for coupled spin-lattice dynamics.

[1] S. R. Tauchert, M. Volkov, D. Ehberger, D. Kazenwadel, M. Evers, H. Lange, A. Donges, A. Book, W. Kreuzpaintner, U. Nowak, P. Baum: Polarized phonons carry angular momentum in ultrafast demagnetization, Nature 602, 73 (2022)
[2] S. Mankovsky, S. Polesya, H. Lange, M. Weißenhofer, U. Nowak, and H. Ebert:
Angula Momentum Transfer via Relativistic Spin-Lattice Coupling from First Principles, Phys. Rev. Lett. 129, 067202 (2022)
[3] M. Weißenhofer, H. Lange, A. Kamra, S. Mankovsky, S. Polesya, H. Ebert, and U. Nowak: Rotationally invariant formulation of spin-lattice coupling in multi-scale modeling, Phys. Rev. B 108, L060404 (2023)
[4] M. Weißenhofer, P. Rieger, M.S. Mrudul, L. Mikadze, U. Nowak, and P. M. Oppeneer: Truly chiral phonons arising fromm chirality selective Magnon-Phonon Coupling, arXiv:2411.03879v1
[5] 2022

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