Monte Carlo study of correlations in quantum spin ladders

We study antiferromagnetic spin-1/2 Heisenberg ladders, comprised of n(c) chains (2 less than or equal to n(c) less than or equal to 6) with ratio J(perpendicular to)/J(parallel to) of inter-chain to intra-chain couplings. The correlation length xi(T) is deduced from measurements of the correlation function. For even n(c), the static structure factor exhibits a peak at a temperature below the corresponding spin gap. Results for isotropically coupled ladders (J(perpendicular to)/J(parallel to) = 1) are compared to those for the single chain and the square lattice. For J(perpendicular to)/J(parallel to) less than or equal to 0.5, the correlation function of the two-chain ladder is in excellent agreement with analytic results from conformal field theory, and xi(T) exhibits simple scaling behavior.