Two interacting particles in the Harper model
  Dynamics of two particles with short range repulsive or attractive interaction is studied numerically in the Harper model. It is shown that interaction leads to appearance of localized states and pure-point spectrum component in the case when noninteractive system is quasi-diffusive or ballistic. In the localized phase interaction gives only stronger localization contrary to the case of two interacting particles in a random potential. 
D. L. Shepelyansky