Movies of the BEC-BKT crossover in a trapped 2D Bose gas (2005)

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Movies of the BEC-BKT crossover in a trapped 2D Bose gas (2005)

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	Thermal Vortex-Pair Creation in 2D Bose-Einstein Condensates T. P. Simula and P. B. Blakie Department of Physics, University of Otago, Dunedin, New Zealand. tapio@physics.otago.ac.nz At ultra-low temperatures dilute 3D Bose gas undergoes Bose-Einstein condensation (BEC) and becomes superfluid. In homogeneous 2D systems, BEC does not occur in the thermodynamic limit and super fluidity is instead achieved through the Berezinskii- Kosterlitz-Thouless (BKT) transition. In the presence of harmonic trapping, however, both BEC and BKT phases have been predicted to co-exist [1,2]. Recently, experimental observation of phase defects in quasi-2D condensates have been reported [3]. We have performed classical field simulations suggesting that the experimentally observed phase defects can be explained in terms of thermally activated vortex-antivortex pairs [2]. The figure below shows computed spatial densities (a,b,c) and the corresponding phase profiles (d,e,f) of the gas at the respective temperatures, T = (0.2, 0.7 and 0.9)T0, below the ideal-gas BEC temperature, T0. The low temperature phase coherent BEC (a,d), and the phase fluctuating BKT (c,f) phases are separated by a vortex-pair creation transition. As temperature is further increased the super fluidity is destroyed at the BKT-normal transition.
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	[1] T. P. Simula, M. D. Lee and D. A. W. Hutchinson, Phil. Mag. Lett 85, 395 (2005). link. [2] T. P. Simula and P. B. Blakie, Phys. Rev. Lett. 96, 020404 (2006). link. [3] S. Stock, Z. Hadzibabic, B. Battelier, M. Cheneau and J. Dalibard, Phys. Rev. Lett. 95, 190403 (2005). link.

	Movies Currently we have two movies of our simulations available in mpeg4 and AVI formats.

	Movie 1: Dynamics of vortex pairs in the BKT phase at constant temperature for the case in Fig.3 of [Phys. Rev. Lett. 96, 020404 (2006)] . [mpeg4 format, 3.7MB] [avi format, 6.7MB]
	Movie 2: Propagation of the BEC-BKT transition as a function of temperature for N=1e4. The diameter of the red circle is one Thomas-Fermi radius. [mpeg4 format, 3.7MB] [avi format, 6.7MB] General Comment: The system parameters are those used in [Phys. Rev. Lett. 96, 020404 (2006)] . The plus and minus signs denote the locations of vortices and antivortices, respectively.


	Paper This research, Thermal activation of vortex-antivortex pairs in quasi-2D Bose-Einstein condensates, T.P. Simula and P. Blair Blakie, is published at [Phys. Rev. Lett. 96, 020404 (2006)]. A preprint is also available: Cond-Mat Archive.