Spatial separation in a thermal mixture of ultracold $^{174}$Yb and   $^{87}$Rb atoms
  We report on the observation of unusually strong interactions in a thermal mixture of ultracold atoms which cause a significant modification of the spatial distribution. A mixture of $^{87}$Rb and $^{174}$Yb with a temperature of a few $\mu$K is prepared in a hybrid trap consisting of a bichromatic optical potential superimposed on a magnetic trap. For suitable trap parameters and temperatures, a spatial separation of the two species is observed. We infer that the separation is driven by a large interaction strength between $^{174}$Yb and $^{87}$Rb accompanied by a large three-body recombination rate. Based on this assumption we have developed a diffusion model which reproduces our observations. 
Florian Baumer, Frank M\"unchow, Axel G\"orlitz, Stephen E. Maxwell,   Paul S. Julienne, Eite Tiesinga
physics.atom-ph cond-mat.quant-gas quant-ph