KTHNY theory
In statistical mechanics, the Kosterlitz–Thouless–Halperin–Nelson–Young (KTHNY) theory describes the process of melting of crystals in two dimensions (2D). The name is derived from the initials of the surnames of John Michael Kosterlitz, David J. Thouless, Bertrand Halperin, David R. Nelson, and A. Peter Young, who developed the theory in the 1970s.