SPIN-SPIN CORRELATION LENGTHS OF BILAYER ANTIFERROMAGNETS

The correlation length and the static structure factor for bilayer ant iferromagnets, such as YBa2Cu3O6, are calculated using field theoretic al and numerical methods. It is shown that these quantities can be dir ectly measured in neutron scattering experiments using energy integrat ed two-axis scan despite the strong intensity modulation perpendicular to the layers. Our calculations show that the correlation length of t he bilayer antiferromagnet diverges considerably more rapidly, as the temperature tends to zero, than the correlation length of the correspo nding single-layer antiferromagnet typified by La2CuO4. This rapid div ergence may have important consequences with respect to magnetic fluct uations of the doped superconductors.