Wannier-Stark states of a quantum particle in 2D lattices
  A simple method of calculating the Wannier-Stark resonances in 2D lattices is suggested. Using this method we calculate the complex Wannier-Stark spectrum for a non-separable 2D potential realized in optical lattices and analyze its general structure. The dependence of the lifetime of Wannier-Stark states on the direction of the static field (relative to the crystallographic axis of the lattice) is briefly discussed. 
M. Glueck, F.Keck, A. R. Kolovsky and H. J. Korsch