Kosterlitz-Thouless transition in the two-dimensional quantumXYmodel

Convincing numerical evidence is obtained via extensive quantum Monte Carlo simulations on square lattices as large as 96×96 that the spin-1/2 XY model undergoes a Kosterlitz-Thouless phase transition at ${\mathit{kT}}_{\mathit{c}}$/J=0.350(4). Correlation length and in-plane susceptibility diverge at ${\mathit{T}}_{\mathit{c}}$ precisely according to the form predicted by Kosterlitz and Thouless for the classical XY model. The specific heat increases very rapidly near ${\mathit{T}}_{\mathit{c}}$ and exhibits a peak around kT/J=0.45.