Effects of Interactions on the Critical Temperature of a Trapped Bose   Gas
  We perform high-precision measurements of the condensation temperature of a harmonically-trapped atomic Bose gas with widely-tuneable interactions. For weak interactions we observe a negative shift of the critical temperature in excellent agreement with mean-field theory. However for sufficiently strong interactions we clearly observe an additional positive shift, characteristic of beyond-mean-field critical correlations. We also discuss non-equilibrium effects on the apparent critical temperature for both very weak and very strong interactions. 
Robert P. Smith, Robert L. D. Campbell, Naaman Tammuz, and Zoran   Hadzibabic
cond-mat.quant-gas cond-mat.stat-mech physics.atom-ph quant-ph