SPIN CORRELATION-FUNCTIONS IN RANDOM-EXCHANGE S=1 2 XXZ CHAINS/

The decay of (disorder-averaged) static spin correlation functions at T = 0 for the one-dimensional spin-1/2 XXZ antiferromagnet with unifor m longitudinal coupling J Delta and random transverse coupling J lambd a(i) is investigated by numerical calculations for ensembles of finite chains, At Delta = 0 (XX model) the calculation is based on the Jorda n-Wigner mapping to free lattice fermions for chains with up to N = 10 0 sites. At Delta not equal 0 Lanczo diagonalizations are carried out for chains with up to N = 22 sites. The longitudinal correlation funct ion [(S0Srz)-S-z] is found to exhibit a power-law decay with an expone nt that varies with Delta and, for nonzero Delta, also with the width of the lambda(i)-distribution. The results for the transverse correlat ion function [(S0Srx)-S-x] show a crossover from power-law decay to ex ponential decay as the exchange disorder is turned on. (C) 1996 Americ an Institute of Physics.