Surface and interface effects on the dielectric polarization and refractive indices of BaTiO<inf>3</inf> single crystals and ultrathin films

Abstract

The surface and interface effects on the dielectric polarization and refractive indices of BaTiO 3 single crystals and BaTiO 3 ultrathin films on SrTiO 3 single crystal substrates are investigated theoretically by using a microscopic model based on the orbital approximation in correlation with the dipole-dipole interaction. The spontaneous polarization of BaTiO 3 single crystals is drastically reduced near the c-surface. For BaTiO 3 /SrTiO 3 films, the spontaneous polarization is reduced in the film 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 single crystals or for BaTiO 3 films and SrTiO 3 substrates to be strongly reduced for light polarized perpendicular to the surface.