Phase transitions of the 6-clock model in two dimensions

It is confirmed that there exists a Kosterlitz-Thouless (KT) like phase in the ferromagnetic 6-clock model on the square lattice through studies of the interfacial free energy estimated by Monte Carlo simulations. The authors find that lower and upper transition temperatures are T1=0.75 and T2=0.90 respectively, and that the critical exponent eta for the correlation function in the KT-like phase varies from 0.15 at T1 to 0.26 at T2. The correlation length zeta just above T2 is estimated directly from the magnetization profile, and it is shown to behave as zeta approximately exp(bt-12/), t=(T-T2)/T2 approaching the KT-like phase.