Defect-Induced Long-Range Order and the Imry–Ma State in 2-D O(n) Models

摘要

The anisotropic distribution of the defect-induced random local field directions in 2-D systems with continuous symmetry of the order parameter ( $O(n)$ models) can induce a global anisotropy of the “easy axis” type which transfers the system to the universality class of Ising models and the long-range order arises in it at finite temperature. At the same time, statistical fluctuations of random defect fields cause the appearance of the disordered Imry–Ma phase in which the order parameter follows fluctuations of the random field. The confrontation of these two opposite trends in 2-D $O(n)$ models with defects of the “random local field” type was investigated, and their phase diagrams were constructed.