Disorder-Induced Superfluidity in Hardcore Bosons in Two Dimensions

We study the effect of disorder on hardcore bosons in two dimensions at the SU(2) symmetric “Heisenberg point”. We obtain our results with quantum Monte Carlo simulations using the directed loop algorithm. In the absence of disorder, the system has no long-range order at finite temperature due to the enhanced symmetry. However, the introduction of a disordered potential, uniformly distributed from −∆ to ∆, induces a finite-temperature superfluid phase. In particular the diagonal correlation length ξ decreases but the superfluid order-parameter correlation function becomes a power-law. A non-monotonic finite-size behavior is noted and explained as arising due to ξ. We provide evidence that at long distances the effects of a weak disordered potential can be mimicked by an effective uniform potential with a root-mean-square value: μeff = ∆/ √ 3. For strong disorder, the system becomes a Bose glass insulator.