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Abstract
The surface effect on the dielectric polarization and refractive indices of BaTiO 3 ultrathin films on SrTiO 3 single crystal substrates is investigated theoretically by using a microscopic model based on the orbital approximation in correlation with the dipole–dipole interaction. The spontaneous polarization of the BaTiO 3 /SrTiO 3 film is reduced as its thickness decreases. However, an electronic polarization appears within the SrTiO 3 substrate in the neighborhood of the interface. This polarization, which vanishes far away from the interface into the SrTiO 3 bulk, is induced by the polarization of the BaTiO 3 film. Furthermore, we find the refractive index either for BaTiO 3 films or for SrTiO 3 substrates to be strongly reduced for light polarized perpendicular to the surface.