KOSTERLITZ-THOULESS TRANSITION IN THE 2-DIMENSIONAL QUANTUM XY MODEL

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 kTc/J=0.350(4). Correlation length and in-plane susceptibility diverge at Tc precisely according to the form predicted by Kosterlitz and Thouless for the classical XY model. The specific heat increases very rapidly near Tc and exhibits a peak around kT/J=0.45. © 1990 The American Physical Society.