Physics – Condensed Matter – Strongly Correlated Electrons
Scientific paper
2009-12-16
Phys. Rev. B 81, 104308 (2010)
Physics
Condensed Matter
Strongly Correlated Electrons
8 pages, 2 figures, final version (minor changes, included references)
Scientific paper
10.1103/PhysRevB.81.104308
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.
Kloss Thomas
Kopietz Peter
Kreisel Andreas
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