RANDOM ISOTROPIC ONE-DIMENSIONAL XY-MODEL

The 1D isotropic s = 1/2 XY-model (N sites), with random exchange inte raction in a transverse random field is considered. The random variabl es satisfy bimodal quenched distributions. The solution is obtained by using the Jordan-Wigner fermionization and a canonical transformation , reducing the problem to diagonalizing an N x N matrix, corresponding to a system of N noninteracting fermions. The calculations are perfor med numerically for N = 1000, and the held-induced magnetization at T = 0 is obtained by averaging the results for the different samples. Fo r the dilute case, in the uniform held limit, the magnetization exhibi ts various discontinuities, which are the consequence of the existence of disconnected finite clusters distributed along the chain. Also in this limit, for finite exchange constants J(A) and J(B), as the probab ility of J(A) varies from one to zero, the saturation field is seen to vary from Gamma(A) to Gamma(B), where Gamma(A) (Gamma(B)) is the valu e of the saturation field for the pure case with exchange constant equ al to J(A) (J(B)). (C) 1998 Elsevier science B.V. All rights reserved.