Phys. Rev. Lett. 126, 137202 (2021)
Spin-Wave Doppler Shift by Magnon Drag in Magnetic Insulators
Tao Yu 1, Chen Wang 2, Michael A. Sentef 1, and Gerrit E. W. Bauer 3
1 Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany
2 Center for Joint Quantum Studies and Department of Physics, School of Science, Tianjin University, Tianjin 300350, China
3 WPI-AIMR and Institute for Materials Research and CSRN, Tohoku University, Sendai 980-8577, Japan
The Doppler shift of the quasiparticle dispersion by charge currents is responsible for the critical supercurrents in superconductors and instabilities of the magnetic ground state of metallic ferromagnets. Here we predict an analogous effect in thin films of magnetic insulators in which microwaves emitted by a proximity stripline generate coherent chiral spin currents that cause a Doppler shift in the magnon dispersion. The spin-wave instability is suppressed by magnon-magnon interactions that limit spin currents to values close to but below the threshold for the instability. The spin current limitations by the backaction of magnon currents on the magnetic order should be considered as design parameters in magnonic devices.