In the last two decades, two‐dimensional systems have been found to exhibit phases and phase transitions unlike any seen in their three‐dimensional counterparts. Quantization of the Hall conductance of an electron gas in a strong magnetic field, localization of electronic wavefunctions in the presence of infinitesimally small amounts of impurities, and infinite‐order phase transitions in magnets and crystals are some examples of unusual phenomena in two dimensions. However, it was not merely a pursuit of the novel and the unexpected that got physicists interested in two‐dimensional systems. In fact, studies of two‐dimensional systems are useful for understanding surfaces of three‐dimensional solids, interfaces between two three‐dimensional phases and anisotropic solids in which the interactions in a plane of symmetry are much stronger than interplane couplings. Moreover, our understanding of why and how behavior of physical systems depends on spatial dimensionality has been enhanced considerably by studies of two‐dimensional systems.
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February 1987
February 01 1987
Electrons and Ions at the Helium Surface
Two‐dimensional arrays of charged particles exhibit plasma oscillations and phase transitions such as crystallization and melting in the low‐density classical limit, but their high‐density quantum regime remains to be explored.
Physics Today 40 (2), 43–50 (1987);