We discuss the nature and sequence of phase transitions in two-dimensional systems with continuous degeneracy, in which other factors must be taken into account in addition to the interaction of point-like topological excitations, namely, the existence of an additional discrete degeneracy (which leads to the possibility of domain wall formation), the removal of accidental degeneracy by fluctuations, the formation of solitons, and the presence of a random potential acting on vortices. Formally, we discuss various modifications of the two-dimensional XY model, while physical objects that can be described by such models are various arrays of superconducting junctions and noncollinear planar antiferromagnets.

PACS: 05.70.Fh, 64.60.Cn, 74.81.Fa, 75.10.Hk, 75.50.Ee (all) DOI: 10.1070/PU2006v049n03ABEH005838 URL: https://ufn.ru/en/articles/2006/3/a/ 000239241100001 2-s2.0-33746371040 2006PhyU...49..225K Citation: Korshunov S E "Phase transitions in two-dimensional systems with continuous degeneracy" Phys. Usp. 49 225–262 (2006) BibTexBibNote ® (generic)BibNote ® (RIS)MedlineRefWorks Оригинал: Коршунов С Е «Фазовые переходы в двумерных системах с непрерывным вырождением» УФН 176 233–274 (2006); DOI: 10.3367/UFNr.0176.200603a.0233