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Physical review. B, Condensed matter

Long-range correlated random magnetic fields in the nonlinear σ model

Mau-chung Chang, Elihu Abrahams

Published Jan 1, 1984• 11 citations
Publisher

Abstract

The effect of the long-range correlated random magnetic fields which behave like $〈h(x)h(y)〉$ $\ensuremath{\sim}\frac{1}{{|x\ensuremath{-}y|}^{d\ensuremath{-}\ensuremath{\sigma}}}$ on the critical phenomena is discussed with the use of the nonlinear $\ensuremath{\sigma}$ model. The crossover between the two critical behaviors dominated by the long-range and short-range disorder fixed points is shown to occur at $(m\ensuremath{-}2)\ensuremath{\sigma}\ensuremath{-}d+4=0$ ($m$ is the spin dimensionality). The critical exponents calculated at the long-range disorder fixed point around the lower critical dimensionality $4+\ensuremath{\sigma}$ are not the same as those in $d\ensuremath{-}2$ expansions in the pure system.

DOI
10.1103/physrevb.29.201

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We study the critical behavior of the q-state Potts model in the presence of quenched random fields, which locally prefer ordering of any one of the q states, and are long-range correlated such that [H(0)H(R${)]}_{\mathrm{av}\mathrm{\ensuremath{\sim}}{R}^{\mathrm{\ensuremath{-}}(d\mathrm{\ensuremath{-}}\ensuremath{\theta})}}$. We find a stable critical behavior controlled by a new random fixed point, and obtain a set of critical exponents within the \ensuremath{\epsilon}\ifmmode \tilde{}\else \~{}\fi{} expansion (\ensuremath{\epsilon}\ifmmode \tilde{}\else \~{}\fi{}=8+\ensuremath{\theta}-d), which cannot be related to those of a pure Potts model of lower dimensionality.
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