Stability Diagrams of a Bose-Einstein Condensate in Excited Bloch Bands

Landau and dynamical instabilities of a Bose-Einstein condensate (BEC) in the excited bands of a one-dimensional optical lattice are investigated by the Gross-Pitaevskii theory. Our results show that there always exists Landau instability for a BEC in the whole region of excited bands.We also map out the dangerous zones of the dynamical instability. The experimental implications of the stability diagram are discussed.