Abstract

A disorder-dependent Gaussian variational approach is applied to the d-dimensional ferromagnetic XY model in a random field. The randomness yields a nonextensive contribution to the variational free energy, implying a random mass term in correlation functions. The Imry-Ma low-temperature result, concerning the existence (d>4) or absence (d<4) of long-range order is obtained in a transparent way. The physical picture which emerges below d=4 is that of a marginally stable mixture of domains. We also calculate within this variational scheme, disorder-dependent correlation functions, as well as the probability distribution of the Imry-Ma domain size.

Publication Type:	Article
Additional Information:	doi: http://dx.doi.org/10.1103/PhysRevB.53.R2941
Subjects:	Q Science > QC Physics
Departments:	School of Policy & Global Affairs > Economics

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