Regensburg 2013 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 9: Quantum Liquids, Miscellaneous 1

TT 9.7: Talk

Monday, March 11, 2013, 11:15–11:30, H21

Thermalization of magnons in yttrium-iron garnet: nonequilibrium functional renormalization group approach — •Johannes Hick¹, Andreas Rückriegel¹, Thomas Kloss², and Peter Kopietz¹ — ¹Institut für Theoretische Physik, Goethe Universität Frankfurt am Main, Germany — ²Laboratoire de Physique et Modélisation des Milieux Condensé, CNRS and Université Joseph Fourier, Grenoble, France

Using a nonequilibrium functional renormalization group (FRG) approach we calculate the time evolution of the momentum distribution of a magnon gas in contact with a thermal phonon bath. As a cutoff for the FRG procedure we use a hybridization parameter Λ giving rise to an artificial damping of the phonons. Within our truncation of the FRG flow equations the time evolution of the magnon distribution is obtained from a rate equation involving cutoff-dependent nonequilibrium self-energies, which in turn satisfy FRG flow equations depending on cutoff-dependent transition rates. Our approach goes beyond the Born collision approximation and takes the feedback of the magnons on the phonons into account. We use our method to calculate the thermalization of a quasi two-dimensional magnon gas in the magnetic insulator yttrium-iron garnet after a highly excited initial state has been generated by an external microwave field. In this material interactions which do not conserve the magnon particle number are present and are considered in our approach.