Lee, J-W; Chandrasekharan, S; Baranger, HU, *Disorder-Induced Superfluidity in Hardcore Bosons in Two Dimensions*
(November, 2006) [0611109v1] .
**Abstract:**

*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 -D to D, induces a finite-temperature superfluid
phase. In particular the diagonal correlation length \xi 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
\xi. 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: mu_eff = D/sqrt{3}. For strong disorder, the system
becomes a Bose glass insulator.*