Kosterlitz-Thouless Transition

The Kosterlitz-Thouless transition is a phenomenon in certain two-dimensional materials where, at low temperatures, vortex-like defects in the material's order form tightly bound pairs, maintaining a form of organized behavior. As temperature increases past a critical point, these pairs unbind, leading to a sudden loss of this order. Unlike typical phase transitions, this transition involves the unbinding of topological defects rather than symmetry breaking, resulting in a gradual change from a superconducting or superfluid state to a disordered phase. It's a fundamental example of a phase change driven by the behavior of vortices in two-dimensional systems.