The system undergoing this phenomenon is equivalent to a (*) Coulomb gas in which winding number has replaced charge.
An experimental confirmation of this phenomenon was done in triangular arrays of lead-tin junctions by Resnick et al. The renormalization group approach to this phenomenon requires using a "flow parameter" to derive normalized stiffness and fugacity equations. The developers of this phenomenon discovered a related melting phenomenon sometimes named for Halperin, Nelson, and Young in which there exists an intermediate hexatic substance. In all systems that undergo this phenomenon, the ratio of the spin-wave stiffness to the temperature of its occurrence is equal to two over pi. The system undergoing this phenomenon is equivalent to a (*) Coulomb gas in which winding number has replaced charge. This phenomenon, which is continuous and therefore has infinite order, can be derived by considering a pair of vortices in a gas binding to and unbinding from each other. For 10 points, name this phase transition that occurs in the two-dimensional XY model of a ferromagnet, in which long range order disappears at high temperatures, named for two physicists.
An experimental confirmation of this phenomenon was done in triangular arrays of lead-tin junctions by Resnick et al.
BKT transition [or Berezinskii-Kosterlitz-Thouless transition]