Correlations and Neel order of randomly diluted quantum spin ladders

We present a Monte Carlo study of the correlation length xi of randomly diluted antiferromagnetic spin-1/2 two-chain Heisenberg ladders with weak and intermediate interchain couplings, J/J less than or equal to 1. We are able to access the experimentally relevant low-temperature regime, T/J approximate to 1/500, and find (i) that the form xi(z, T) = A(z) + B(z)T-v, with v = 0.40(5), describes our data at low and moderate dilution z and up to rather high temperatures, (ii) evidence for scaling of xi J/J in the variable zJ/J at weak J/J, (iii) an enhancement of correlations that is strongest for a fraction z approximate to J/(8J) of dilutants, and (iv) that the Neel temperature of Sr(Cu1-xZnz)(2)O-3 corresponds well to a curve of constant correlation length xi = 18(2) of the single diluted ladder with J/J less than or equal to 1/2.