Localized states and interaction induced delocalization in Bose gases   with quenched disorder
  Very diluted Bose gas placed into a disordered environment falls into a fragmented localized state. At some critical density the repulsion between particles overcomes the disorder. The gas transits into a coherent superfluid state. In this article the geometrical and energetic characteristics of the localized state at zero temperature and the critical density at which the quantum phase transition from the localized to the superfluid state proceeds are found. 
G.M. Falco, T. Nattermann and V.L. Pokrovsky