Quantum Phase Transitions of Hard-Core Bosons in Background Potentials
  We study the zero temperature phase diagram of hard core bosons in two dimensions subjected to three types of background potentials: staggered, uniform, and random. In all three cases there is a quantum phase transition from a superfluid (at small potential) to a normal phase (at large potential), but with different universality classes. As expected, the staggered case belongs to the XY universality, while the uniform potential induces a mean field transition. The disorder driven transition is clearly different from both; in particular, we find z~1.4, \nu~1, and \beta~0.6. 
Anand Priyadarshee, Shailesh Chandrasekharan, Ji-Woo Lee, and Harold   U. Baranger