Spin-Wave Doppler Shift by Magnon Drag in Magnetic Insulators

Tao Yu, Chen Wang, Michael A. Sentef, Gerrit E. W. Bauer

Published 2020-11-30Version 1

Doppler shift of quasiparticle dispersion induced by charge currents is responsible for the critical supercurrents in superconductors and spin-wave instabilities by spin-transfer torque in metallic ferromagnets. Here we predict an analogous effect in thin films of magnetic insulators. A coherent spin current, excited by stripline microwaves, or a thermal magnon current, driven by a temperature gradient, can induce a Doppler shift that tilts the magnon dispersion in the spin-current direction. Around a critical driving strength, that is characterized by a spin-wave instability in the self-consistent mean-field treatment, the pumped magnon current reaches a maximum accompanied by a strong breaking of chiral pumping. The backaction of magnon currents on magnetic orders is therefore important for realizing large spin currents in low-dimensional magnonic devices.