LOW-TEMPERATURE PHASE OF THE 2-DIMENSIONAL QUANTUM XY MODEL

Quantum Monte Carlo simulation is used to study static properties of the two-dimensional spin-1/2 XY model on a square lattice. We measured spin correlations, zero-momentum static structure factor, spin stiffness, and vortex density. By testing the universal predictions of the theory, we show that our computation supports the theoretical picture of Kosterlitz and Thouless based on the existence of a line of spin-wave fixed points, and, therefore, the universality class does not change as one goes from the classical to the extreme quantum limit.