CRYSTALLIZATION OF POLARONS IN DOPED IONIC MATERIALS

Large polarons are observed in dielectric materials. Since they have repulsive interactions when the dielectric constants satisfy proper conditions, we propose a model for the crystallization of polarons at low doping concentrations. We calculate the energy at T=0 K and discuss the stability as regards to carriers’ density. With phonons having low frequencies, an instability is related to the polaron dissociation, and we estimate a critical doping density. Applying our model to La 2− x Sr x CuO 4 , we find a good agreement with the experimental critical doping concentration x c ≈0.06 for the insulator-to-metal transition.

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