BOSE-GLASS AND MOTT-INSULATOR PHASE IN THE DISORDERED BOSON HUBBARD-MODEL

We study the two-dimensional disordered boson Hubbard model via quantu m Monte Carlo simulations. It is shown that the probability distributi on of the local susceptibility has a 1/chi(2) tail in the Bose-glass p hase. This gives rise to a divergence although particles are completel y localized here as we prove with the help of the participation ratio. We demonstrate the presence of an incompressible Mott lobe within the Bose-glass phase and show that a direct Mott-insulator-to-superfluid transition happens at the tip of the lobe. Here we find critical expon ents z=1, nu similar to 0.7 and eta similar to 0.1, which agree with t hose of the pure three-dimensional classical XY model.