IMPURITY-INDUCED ANTIFERROMAGNETISM IN SPIN-1 2 HEISENBERG 2-LEG LADDER SYSTEMS/

Based on the phase Hamiltonian representation of a spin-1/2 Heisenherg two-leg ladder system coupled antiferromagnetically, which has a spin gap if clean, it is shown that a non-magnetic impurity replacing a sp in induces a staggered spin modulation. This results in the long range order of antiferromagnetism in the presence of three-dimensional coup ling between the ladders. This will be in accordance with a recent exp erimental observation by Azuma et al. on Sr(Cu1-xZnx)(2)O-3.