Аннотация

The static and dynamic properties of the isotropic XY-model (s = 1/2) on the inhomogeneous periodic chain, composed of N segments with n different exchange interactions and magnetic moments, in a transverse field h, are obtained exactly at arbitrary temperatures. The properties are determined by introducing the generalized Jordan - Wigner transformation and by reducing the problem to a diagonalization of a finite matrix of nth order. The diagonalization procedure is discussed in detail and the critical behaviour induced by the transverse field, at T = 0, is presented. The quantum transitions are determined by analyzing the behaviour of the induced magnetization, defined as (1/n) Sigma(n)(m=1) mu(m) S-j,m(z) where mu(m) is the magnetic moment at site in within the segment j, as a function of the field, and the critical fields determined exactly. The dynamic correlations, S-j,m(z)(t)S-j,m(z) (0), and the dynamic susceptibility chi(zz)(q)(omega) are also obtained at arbitrary temperatures. Explicit results are presented in the limit T = 0, where the critical behaviour occurs, for the static susceptibility chi(zz)(q)(0) as a function of the transverse field h, and for the frequency dependency of dynamic,q susceptibility chi(zz)(q)(omega). Also in this limit, the transverse time-correlation (S-j,m(x)(t)S-j,m'(x)(0)) and the dynamic and isothermal susceptibilities, chi(xx)(q)(omega) and chi(xx)(T), are obtained for the transverse field greater or equal than the saturation field. (C) 2005 Elsevier B.V. All rights reserved.

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