Effects of diagonal disorder on charge density wave and superconductivity in local pair systems

We analyse the influence of diagonal disorder (random site energy) on charge density wave (CDW) and superconductivity (SS) in local pair systems which are described by the model of hard core charged bosons on a lattice. This problem was previously studied within the mean field approximation for the case of half-filled band ( n=1). Here we extend that investigation to the case of arbitrary particle concentration (0< n<2) and examine the phase diagrams of the model and the behaviour of superfluid density ( ρ_s) as a function of n and the increasing disorder. Depending on the strength of random on-site energies, the intersite density-density repulsion and the concentration, the model can exhibit several various phases, including homogeneous phases: CDW, SS and Bose-glass (NO) as well as the phase separated states: CDW-SS, CDW-NO and particle droplets. The obtained results for SS phase are in qualitative agreement with the available Monte-Carlo calculations for two-dimensional lattice. Also, in a definite range of parameters, the system exhibits the phenomena which we call a disorder induced superconductivity and a disorder induced charge ordering.