The Surface or Interface Polaron in Polar Crystals. III. The Phase‐Transition‐Like Transition for the Surface Polaron

The behaviour of the surface polarons in polar crystals is taken into account by making use of the Bogolyubov inequality. The results show that the ground state energy, effective mass, and the effective potential energy of the surface polarons are dependent on the temperature. For the strong coupling surface polaron, when the temperature approaches a certain critical value T 0 , there exists a phase transition from the polaron to the free electron; but for the weak coupling case, such a phase transition does not exist.