| dc.description.abstract | More than ten years ago, Bose-Einstein condensation (BEC) of magnons (or quantized spin
waves) was experimentally observed in yttrium iron garnet (YIG) films at room temperature.
Since BEC and superfluidity are closely related phenomena, it is natural to ask whether such
magnon condensates can transport as superfluid and, if so, how such superfluid looks like. In
this work, we study theoretically superfluidity of magnons in ferromagnetic films. We first give
an review of the basic theory of magnons in ferromagnetic films. We then discuss BEC of
magnons from both experimental and theoretical points of view. Then we study superfluidity of
magnons in ferromagnetic films by starting from a model of spins in ferromagnetic films. Model
in terms of magnon operators is then introduced, and a Hamiltonian describing the condensed
magnons is derived. Focusing on the one-dimensional (1D) stationary case, we study behaviors
of superfluid formed by the condensed magnons. We found an unconventional soliton-like profile
of the magnon superfluid, as compared to a uniform superflow, which we argued to be due to the
dipolar interaction. We also show by estimates that in YIG films it is possible to have a superfluid
current that strongly exceeds the current of normal magnons, so the magnon superfluidity could
possibly be observed. | en |
