Effect of magnon decays on parametrically pumped magnons

TL;DR

This paper studies how magnon decays affect the behavior of parametrically excited magnons in YIG, explaining experimental observations through kinetic equations that incorporate microscopic decay processes.

Contribution

It introduces a microscopic kinetic model that accounts for magnon decays, successfully explaining experimental enhancements in spin pumping near decay thresholds.

Findings

Quantitative agreement with experimental data

Magnon decays significantly influence non-equilibrium magnon dynamics

Enhanced spin pumping observed near decay thresholds

Abstract

We investigate the influence of magnon decays on the non-equilibrium dynamics of parametrically excited magnons in the magnetic insulator yttrium-iron garnet (YIG). Our investigations are motivated by a recent experiment by Noack et al. [Phys. Status Solidi B 256, 1900121 (2019)] where an enhancement of the spin pumping effect in YIG was observed near the magnetic field strength where magnon decays via confluence of magnons becomes kinematically possible. To explain the experimental findings, we have derived and solved kinetic equations for the non-equilibrium magnon distribution. The effect of magnon decays is taken into account microscopically via collision integrals derived from interaction vertices involving three powers of magnon operators. Our results agree quantitatively with the experimental data.