T = 0.80
5 sweeps
Vortices (+)—
Antivortices (−)—
Bound pairs—
Mean energy/site—
vortex (+1)
antivortex (−1)
Below T_BKT, vortices bind in pairs. Above, they unbind (free vortices proliferate), destroying quasi-long-range order. Color encodes spin angle θ ∈ [0, 2π].