Heidelberg 2015 – wissenschaftliches Programm
A 41.9: Vortrag
Freitag, 27. März 2015, 13:00–13:15, M/HS1
Bose-Einstein condensation in classically frustrated optical lattices — •Peter Janzen1,2, Wen-Min Huang1,2,3, and Ludwig Mathey1,2,3 — 1Zentrum für Optische Quantentechnologien, Universität Hamburg, 22761 Hamburg, Germany — 2Institut für Laserphysik, Universität Hamburg, 22761 Hamburg, Germany — 3The Hamburg Centre for Ultrafast Imaging, Luruper Chaussee 149, Hamburg 22761, Germany
We investigate Bose-Einstein condensation in a classically frustrated triangular lattice geometry, as realized recently in experiment . In this system, the single particle dispersion has two distinct minima in the Brillouin zone. Therefore, in addition to a continuous U(1) symmetry, a discrete Z2 symmetry can be broken upon condensation. We derive a general effective action for systems with these symmetries. Using a renormalization group approach, we investigate the critical behavior of this effective action. We find that for the triangular lattice geometry, the condensed state breaks the Z2 symmetry. Also, we find that the transition is of first order, unlike Bose-Einstein condensation in free space, which is a continuous phase transition.
 J. Struck, M. Weinberg, C. Ölschläger, P. Windpassinger, J. Simonet, K. Sengstock, R. Höppner, P. Hauke, A. Eckardt, M. Lewenstein, and L. Mathey, Nature Physics 9, 738 (2013).