Berezinskii-Thouless-Kosterlitz Transition in a Two-Dimensional Atomic Gas

We introduce the concepts of Berezinskii-Kosterlitz-Thouless (BKT) transition and quasi longrange order in the context of the 2D electron gas model. We then apply this framework to 2D superfluidity to obtain the superfluid transition temperature. Finally, we review the recent experimental work of Hadzibabic et al. which observes BKT transition in a 2D trapped Rb gas. Thermal de Broglie wavelength at the critical temperature is reported to be ρCλ 2 = 6 ± 2, in comparison to the theoretical result of ρSλ 2 = 4, where ρC is the condensate density and ρS is the superfluid density.