Parametric pumping and kinetics of magnons in dipolar ferromagnets

Abstract

The time evolution of magnons subject to a time-dependent microwave field is usually described within the so-called "S-theory", where kinetic equations for the distribution function are obtained within the time-dependent Hartree-Fock approximation. To explain the recent observation of "Bose-Einstein condensation of magnons" in an external microwave field [Demokritov et al., Nature 443, 430 (2006)], we extend the "S-theory" to include the Gross-Pitaevskii equation for the time-dependent expectation values of the magnon creation and annihilation operators. We explicitly solve the resulting coupled equations within a simple approximation where only a single condensed mode is retained. We also re-examine the usual derivation of an effective boson model from a realistic spin model for yttrium-iron garnet films and argue that in the parallel pumping geometry (where both the static and the time-dependent magnetic field are parallel to the macroscopic magnetization) the time-dependent Zeemann energy cannot give rise to magnon condensation.

8 pages, 2 figures, final version (minor changes, included references)

References in corpus (5)

• Theory of coherence in Bose-Einstein condensation phenomena in a microwave driven interacting magnon gas
• Stability of Bose Einstein condensates of hot magnons in YIG
• Microscopic spin-wave theory for yttrium-iron garnet films
• Twenty years of magnon Bose condensation and spin current superfluidity in 3He-B
• U(1)-Symmetry breaking and violation of axial symmetry in TlCuCl3 and other insulating spin systems

Cited by in corpus (13)

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• Josephson and Persistent Spin Currents in Bose-Einstein Condensates of Magnons
• Brillouin light scattering spectroscopy of parametrically excited dipole-exchange magnons
• Spin Currents and Magnon Dynamics in Insulating Magnets
• Rayleigh-Jeans condensation of pumped magnons in thin film ferromagnets
• Bose-Einstein condensation at finite momentum and magnon condensation in thin film ferromagnets
• Non-equilibrium time evolution of bosons from the functional renormalization group
• Bose-Einstein Condensation of Nonequilibrium Magnons in Confined Systems
• Parametrically driven THz magnon-pairs: predictions towards ultimately fast and minimally dissipative switching
• Effect of magnon decays on parametrically pumped magnons
• Collisionless kinetic theory for parametrically pumped magnons
• Mechanism for a Chemical Potential of Nonequilibrium Magnons in Parametric Parallel Pumping
• Nonlinear Radiation Damping of Nuclear Spin Waves and Magnetoelastic Waves in Antiferromagnets