XY model

The 2D classical XY model and the topological Kosterlitz-Thouless transition: the vortex energy-entropy argument and vortex unbinding.

Kosterlitz and Thouless: the vortex energy-entropy argument

Kosterlitz and Thouless: the vortex energy-entropy argument

The Kosterlitz-Thouless transition: vortex-antivortex unbinding

The Kosterlitz-Thouless transition: vortex-antivortex unbinding