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 charg e 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 (rho (s)) as a function of n and the increasing disorder. Depending on the strength of r andom on-site energies, the intersite density-density repulsion and the con centration, the model can exhibit several various phases, including homogen eous phases: CDW, SS and Bose-glass (NO) as well as the phase separated sta tes: CDW-SS, CDW-NO and particle droplets. The obtained results for SS phas e 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 c harge ordering. (C) 2001 Elsevier Science B.V. All rights reserved.