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arXiv:1602.06789

Critical behaviour of anisotropic magnets with quenched disorder: replica symmetry breaking studied by operator product expansion

Eugene Kogan, M. Kaveh

Published Feb 22, 2016• 0 citations
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Abstract

We study critical behaviour of disordered magnets near four dimensions. We consider the system with explicit cubic anisotropy and scalar disorder and that with random direction of anisotropy axis. The quenched disorder is taken into account by replica method. Using the method of operator product expansion, we derive in the first order to $ε$ approximation the renormalization group equations taking into account possible replica symmetry breaking.

DOI
10.48550/arxiv.1602.06789

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We study critical behaviour of disordered magnets near four dimensions. We consider the system with explicit cubic anisotropy and scalar disorder and that with random direction of anisotropy axis. The quenched disorder is taken into account by replica method. Using the method of operator product expansion, we derive in the first order to εεε approximation the renormalization group equations taking into account possible replica symmetry breaking.
We study critical behaviour of disordered magnets near four dimensions. We consider the system with explicit cubic anisotropy and scalar disorder and that with random direction of anisotropy axis. The quenched disorder is taken into account by replica method. Using the method of operator product expansion, we derive in the first order to ϵ\epsilonϵ approximation the renormalization group equations taking into account possible replica symmetry breaking.
The critical behaviour of an m -vector model with a local anisotropy axis of random orientation is studied within the field-theoretical renormalization group approach for cubic distribution of anisotropy axis.Expressions for the renormalization group functions are calculated up to the two-loop order and investigated both by an ε = 4 -d expansion and directly at space dimension d = 3 by means of the Pad é-Borel resummation.One accessible stable fixed point indicating a 2nd order ferromagnetic phase transition with dilute Ising-like critical exponents is obtained.
A renormalization-group approach is used for investigating the effects of the Parisi replica symmetry breaking (``spin-glass effects'') on critical properties of d-dimensional systems with extended quenched disorder along ${\ensuremath{\varepsilon}}_{d}$ directions. Within a double expansion scheme to first order in $(\ensuremath{\varepsilon}=4\ensuremath{-}d, {\ensuremath{\varepsilon}}_{d})$ it is found that for $d<~4+{\ensuremath{\varepsilon}}_{d}$ and order-parameter dimensionalities n< 4,n<~4,n< 4, a full fixed-point instability with a consequent runaway towards a strong-coupling regime occurs in the parameter space while, for d<4d<4d<4 and n>4,n>4,n>4, compatibly with the modified Harris criterion, an additional marginally stable fixed point exists which might control a new anisotropic random critical behavior. In any case, the traditional replica-symmetric Dorogovtsev-like solution for classical and quantum systems is unstable against the replica symmetry-breaking modes.
By means of the renormalisation-group approach, static and dynamic critical behaviours are studied for the XY spin system with cubic anisotropy and with quenched random nonmagnetic impurities. The stability of the quenched-random-impurity fixed point in d ( identical to 4- epsilon ) dimensions, the flow diagram of the interactions and the critical exponents are investigated, within the two-loop approximation, in terms of the epsilon 1/2 expansion. It is shown that the transition that appears is a first-order transition.
A eld-theoretic description of the critical behaviour of the weakly disordered systems is given.Directly, for three-and two-dimensional systems a renormalization analysis of the eective Hamiltonian of the model with replica symmetry breaking (RSB) potentials is carried out in the two-loop approximation.For the case with rst-step RSB the xed points (FPs) corresponding to the stability of the various types of critical behaviour are identi ed with the use of the Pad e{Borel summation technique.The analysis of FPs has shown a stability of the critical behaviour of the weakly disordered three-and two-dimensional systems with respect to RSB eects and realization of the former scenario of disorder in uence on critical behaviour.For the case of systems with arbitrary dimension from 3 to 4 the ranges of critical behaviour determined by the RSB eects are found for each value of the p-component order parameter without the use of "-expansion.A comparison with the results of the "-expansion calculations is carried out.
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