CORRELATION LENGTH FROM CLUSTER-DIAMETER DISTRIBUTION

We report numerical estimates of correlation lengths in 2D Potts model s from the asymptotic decay of the cluster-diameter distribution. Usin g this observable we are able to verify theoretical predictions for th e correlation length in the disordered phase at the transition point f or q = 10, 15, and 20 with an accuracy of about 1% - 2%. This is a con siderable improvement over previous measurements using the standard (p rojected) two-point function.