MEAN-FIELD HOPPING APPROACH OF DISORDERED INTERACTING BOSONS

We study the interplay between disorder (W) and interaction (U) in a b oson Anderson-Hubbard model. Using a mean-field hopping (t) approach, we calculate the free energy and we obtain the metal-insulator phase d iagram for a system in which the number of bosons is equal to the numb er of sites. At zero temperature, we study the critical value of hoppi ng (t(c)) as a function of W/U. For t > t(c), the ground state gives t he metallic phase (M). For t < t(c), two different insulating phases a re distinguished: (I) for small disorder (W/U < 0.5), the ground state is a Mott insulator (H); (II) for large disorder (W/U > 0.5), the gro und state shows a Bose glass insulator (B). Starting from the H, and i ncreasing W we obtain first an insulator-to-metal transition, and then a second transition into the B phase. At finite temperature, we study the critical temperature (T-c) vs U for different values of W, in uni ts of t. We obtain two different transitions when U is increased: star ting from the insulating phase, we find first an insulator-to-metal tr ansition, and then a second transition into the insulating phase. Also , at low temperatures, the phase diagram shows a metallic reentrant be havior: the temperature-induced insulator-to-metal-to-insulator transi tions. Copyright (C) 1996 Elsevier Science Ltd