Dresden 2011 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 37: MLT: Quantum Liquids, Bose-Einstein Condensates, Ultra-cold Atoms, ...
TT 37.8: Talk
Wednesday, March 16, 2011, 16:00–16:15, HSZ 105
Bose-Einstein condensation at finite momentum and magnon condensation in thin film ferromagnets — •Johannes Hick, Francesca Sauli, Andreas Kreisel, and Peter Kopietz — Institut für Theoretische Physik, Universität Frankfurt, Max-von-Laue Strasse 1, 60438 Frankfurt, Germany
We use the Gross-Pitaevskii equation to determine the spatial structure of the condensate density of interacting bosons whose energy dispersion єk has two degenerate minima at finite wave-vectors ± q. We show that in general the Fourier transform of the condensate density has finite amplitudes for all integer multiples of q. If the interaction is such that many Fourier components contribute, the Bose condensate is localized at the sites of a one-dimensional lattice with spacing 2π/|q|; in this case Bose-Einstein condensation resembles the transition from a liquid to a crystalline solid. We use our results to investigate the spatial structure of the Bose condensate formed by magnons in thin films of yttrium-iron garnet .