Wang, YC (reprint author), Beijing Normal Univ, Dept Phys, Beijing 100875, Peoples R China.
We present a quantum Monte Carlo study of the "quantum glass" phase of the two-dimensional Bose-Hubbard model with random potentials at filling rho = 1. In the narrow region between the Mott and superfluid phases, the compressibility has the form kappa similar to exp(-b/T alpha) + c with a < 1 and c vanishing or very small. Thus, at T = 0 the system is either incompressible (a Mott glass) or nearly incompressible (a Mott-glass-like anomalous Bose glass). At stronger disorder, where a glass reappears from the superfluid, we find a conventional highly compressible Bose glass. On a path connecting these states, away from the superfluid at larger Hubbard repulsion, a change of the disorder strength by only 10% changes the low-temperature compressibility by more than 4 orders of magnitude, lending support to two types of glass states separated by a phase transition or a sharp crossover.
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