We have observed phase defects in quasi-2D Bose-Einstein condensates close to the condensation temperature. Either a single or several equally spaced condensates are produced by selectively evaporating the sites of a 1D optical lattice. When several clouds are released from the lattice and allowed to overlap, dislocation lines in the interference patterns reveal nontrivial phase defects.
@article{arxiv.cond-mat/0506559,
title = {Observation of Phase Defects in Quasi-2D Bose-Einstein Condensates},
author = {Sabine Stock and Zoran Hadzibabic and Baptiste Battelier and Marc Cheneau and Jean Dalibard},
journal= {arXiv preprint arXiv:cond-mat/0506559},
year = {2009}
}