Role of interactions in 87Rb-40K Bose-Fermi mixtures in a 3d optical   lattice
  We investigate the effect of interspecies interaction on a degenerate mixture of bosonic 87Rb and fermionic 40K atoms in a three-dimensional optical lattice potential. Using a Feshbach resonance, the 87Rb-40K interaction is tuned over a wide range. Through an analysis of the 87Rb momentum distribution, we find a pronounced asymmetry between strong repulsion and strong attraction. In the latter case, the Bose-Hubbard parameters are renormalized due to self-trapping, leading to a marked shift in the superfluid to Mott insulator transition with increasing Bose-Fermi interaction. 
Th. Best, S. Will, U. Schneider, L. Hackermueller, D.-S. Luehmann, D.   van Oosten, and I. Bloch