The Pockels Response in Low-Temperature Rhombohedral BaTiO₃

The linear electro-optic (EO), or Pockels, effect can bridge upcoming optical technology with conventional silicon devices. Si-integrated barium titanate (BTO) is a promising material for EO modulators in silicon photonics, but little is known about its low-temperature phases. Understanding the lowest-temperature phase (rhombohedral) is critical for certain fields, such as optical quantum computing, that require cryogenic conditions. In this talk, we report a first principles analysis built on density functional perturbation theory, exploring the origins of a strong Pockels response by examining the components that make up the ionic contribution to the electro-optic tensor. We identify the phonon modes dominating the response and establish their relation to the electronic structure and optical properties. We also consider the role strain plays in enhancing the response.