2D XY model — continuous spins on a lattice. At low temperature, spins align. Near the Kosterlitz-Thouless transition, topological vortices and anti-vortices appear and unbind.
0.80
0.0
10
Energy: — · Magnetization: — · Vortices: —
Metropolis algorithm · KT transition at T_c≈0.89 (J=1) · arrows show spin direction