Degenerate Bose-Bose mixture in a three-dimensional optical lattice

We produce a heteronuclear quantum degenerate mixture of two bosonic species, (87)Rb and (41)K, in a three-dimensional optical lattice. On raising the lattice barriers, we observe the disappearance of the inference pattern of the heavier (87)Rb, shifting toward shallower lattice depths in the presence of a minor fraction of (41)K. This effect is sizable and requires only a marginal overlap between the two species. We compare our results with similar findings reported for Fermi-Bose mixtures and discuss the interpretation scenarios proposed to date, arguing that the explanation may be linked to the increased effective mass due to the interspecies interactions.