Long-range order in two dimensions

Abstract Determining what kind of long-range ordering, if any, exists in continuous symmetry systems at two dimensions (2D) is one of the current intriguing problems in condensed matter physics.′ This is because of the fundamental interest in this problem, in which fluctuations play an extremely important role, as well as the fact that many experimentally accessible systems which are approximately 2D are becoming available. A particular subclass of the latter‐adsorbed molecules and monolayers2 on a clean substrate —is related to developments in surface physics techniques and may even suggest ideas of practical importance. Also, several bio‐physical systems have lower‐D structures,3 although it remains to be seen whether fluctuations of the kind to be discussed here have a real biophysical relevance.