Phase transition of the six-state clock model observed from the entanglement entropy

The Berezinskii-Kosterlitz-Thouless (BKT) transitions of the six-state clock model on the square lattice are investigated by means of the corner-transfer matrix renormalization group method. The classical analogue of the entanglement entropy $S( L, T )$ is calculated for $L$ by $L$ square system up to $L = 129$, as a function of temperature $T$. The entropy has a peak at $T = T^{*}_{~}( L )$, where the temperature depends on both $L$ and boundary conditions. Applying the finite-size scaling to $T^{*}_{~}( L )$ and assuming the presence of BKT transitions, the transition temperature is estimated to be $T_1^{~} = 0.70$ and $T_2^{~} = 0.88$. The obtained results agree with previous analyses. It should be noted that no thermodynamic function is used in this study.