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Journal of Physics A Mathematical and General

Local magnetisation of the n-vector model with a large-scale defect in the limit n to infinity

R. Z. Bariev, Ilyas Z. Ilaldinov

Published Sep 21, 1989• 2 citations
Publisher

Abstract

The local magnetisation of the three-dimensional n-vector model is studied near the large-scale d'-dimensional defect in the limit n to infinity . The model is characterised by the fact that the spin lengths close to the defect are changed as S r 2 =n(1- lambda /r) with the distance r from the defect. It is shown that near the critical point the local magnetisation exhibits a nonuniversal behaviour if d'=0, 1 and a nonscaling behaviour if d'=2. In the first case the critical exponents beta ' and nu ' are calculated up to the order of lambda and it is shown that these exponents satisfy the usual scaling law relations up to this order.

DOI
10.1088/0305-4470/22/18/006

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The local magnetisation of the three-dimensional n-vector model is studied near the large-scale d'-dimensional defect in the limit n to infinity . The model is characterised by the fact that the spin lengths close to the defect are changed as S r 2 =n(1- lambda /r) with the distance r from the defect. It is shown that near the critical point the local magnetisation exhibits a nonuniversal behaviour if d'=0, 1 and a nonscaling behaviour if d'=2. In the first case the critical exponents beta ' and nu ' are calculated up to the order of lambda and it is shown that these exponents satisfy the usual scaling law relations up to this order.
The correlation functions of the three-dimensional n-vector model are studied near the large-scale d'-dimensional defect in the limit n to infinity . The model is characterised by the fact that the spin lengths close to the defect are changed with respect to their bulk value. The deviations decay as - lambda /r with the distance r from the defect. It is shown that at the critical point the correlation function exhibits nonscaling behaviour if d'=2 and nonuniversal behaviour if d'=1. The deviation of a critical exponent eta is calculated up to order of lambda .
The n-vector model in a d-dimensional lattice is studied where a d′-dimensional defect exists. The defect is defined in such a way that the spin length there is different from that in other parts. The pair correlation function in the defect space is discussed in the limit n→∞. It is shown that if d′=2 a critical exponent η• pertaining to the critical correlation is nonuniversal; it does depend on λ where λ is a parameter describing the strength of defect. The η′ is calculated up to order of λ.
The local critical behavior of the ddd-dimensional nnn-vector model near an internal $d\ensuremath{-}1$ dimensional plane of weakened interactions in the limit $n\ensuremath{\rightarrow}\ensuremath{\infty}$ changes qualitatively at d=3d=3d=3. For d>3d>3d>3 the critical exponent ${\ensuremath{\eta}}_{\ensuremath{\parallel}}$, which characterizes the correlation of spins in the defect plane, is universal, i.e., is independent of the strength of the interactions in the defect plane. We argue that ${\ensuremath{\eta}}_{\ensuremath{\parallel}}$ is nonuniversal for d=3d=3d=3 and calculate its dependence on the difference between the defect and bulk couplings to second order in perturbation theory. We show that the excess energy density at a distance zzz from the defect plane decays at the critical point to the bulk value as ${z}^{\ensuremath{-}2}$ for $d\ensuremath{\ge}3$ and faster than ${z}^{\ensuremath{-}2}$ for d<3d<3d<3. Near the free surface of a semi-infinite system one finds a ${z}^{\ensuremath{-}2}$ dependence for d>3d>3d>3 as well as for $d\ensuremath{\ge}3$.