Phase diagram of the quantum O(2)-model in 2+1 dimensions

Understand

The quantum O(2) model in 2+1 dimensions is studied by simulating the 3d O(2) model near criticality.

• Finite densities are introduced by a non-zero chemical potential mu, and the worm algorithm is used to circumvent the sign problem.
• The renormalisation is discussed in some detail.
• We find that the onset value of the chemical potential coincides with the mass gap.