Orientational order of the two-dimensional hard-disk system

We report Monte Carlo results for the two-dimensional hard-disk system. Simulations were performed in the NVT ensemble with up to 65 536 disks, using a new updating scheme. We analyze the bond orientational order parameter and correlation length in the isotropic phase and the scaling behaviour of the bond orientational order parameter in the transition region. The data are consistent with predictions of the Kosterlitz-Thouless-Halperin-Nelson-Young theory, while a first-order phase transition is unlikely and a one-stage continuous transition can be ruled out.