THE CORRELATION LENGTH OF THE POTTS-MODEL AT THE 1ST-ORDER TRANSITIONPOINT

We consider the Q-state two-dimensional Potts model for Q > 4, i.e. in the first-order phase transition regime, Following a scheme given by P Martin, we prove an identity between the spectra of the transfer mat rices of the Potts model and the transfer matrices connecting the diag onals of a 6-vertex model. By using a Bethe ansatz for the latter, we obtain an exact expression for the correlation length of the Potts mod el at the transition point.