Possibility of direct Mott insulator-to-superfluid transitions in weakly disordered boson systems

Abstract

We study the zero-temperature phase transitions of a two-dimensional disordered boson Hubbard model at incommensurate boson densities. Via matrix diagonalization and quantum Monte Carlo simulations, we construct the phase diagram and evaluate the correlation length exponent v. In the presence of weak disorder, we obtain v = 0.5 +/- 0.1, the same value as that in the pure model, near the tip of a Mott insulator lobe, using the dynamical critical exponent z = 2. As the strength of disorder is increased beyond a certain value, however, the value of v is found to change to 0.9 +/- 0.1. This result strongly suggests that there exist direct Mott insulator-to-superfluid transitions around the tip of a Mott insulator lobe: in the weak disorder regime. [S0163-1829(99)08513-6].