Monte Carlo study of an improved clock model in three dimensions

We study a generalized clock model on the simple cubic lattice. The parameter of the model can be tuned such that the amplitude of the leading correction to scaling vanishes. In the main part of the study we simulate the model with $Z_8$ symmetry. At the transition, with increasing length scale, $O(2)$ symmetry emerges. We perform Monte Carlo simulations using a hybrid of local Metropolis and cluster algorithms of lattices with a linear size up to $L=512$. The field variable requires less memory and the updates are faster than for a model with $O(2)$ symmetry at the microscopic level. Our finite size scaling analysis yields accurate estimates for the critical exponents of the three-dimensional XY-universality class. In particular we get $\eta=0.03810(8)$, $\nu=0.67169(7)$, and $\omega=0.789(4)$. Furthermore we obtain estimates for fixed point values of phenomenological couplings and critical temperatures.