Topological Defects — XY Model

Berezinskii-Kosterlitz-Thouless transition — vortices and antivortices
vortices: 0 | antivortices: 0 | T = 1.00 | Click to add vortex
Temperature (T/J)

1.00
Steps/Frame

10
Spin Display

Arrows
The XY model places a planar spin (angle θ ∈ [0,2π)) on each lattice site. At low temperature, spins align and vortex-antivortex pairs are bound. Above the BKT transition temperature (~0.89 J/k_B for 2D XY), pairs unbind and proliferate, destroying quasi-long-range order. Red dots = vortices (winding +1), blue dots = antivortices (−1). Colors on left canvas show spin angle.