Thickness Control of the Spin-Polarized Two-Dimensional Electron Gas in LaAlO₃/BaTiO₃ Superlattices

We explored the possibility of increasing the interfacial carrier quantum confinement, mobility and conductivity in the (LaAlO₃)_n/(BaTiO₃)_n superlattices by thickness regulation using the first-principles electronic structure calculations. Through constructing two different interfacial types of LaAlO₃/BaTiO₃ superlattices, we discovered that the LaO/TiO₂ interface is preferred from cleavage energy consideration. We then studied the electronic characteristics of two-dimensional electron gas (2DEG) produced at the LaO/TiO₂ interface in the LaAlO₃/BaTiO₃ superlattices via spin-polarized density functional theory calculations. The charge carrier density of 2DEG has a magnitude of 10¹⁴ cm^-2 (larger than the traditional system LaAlO₃/SrTiO₃), which is mainly provided by the interfacial Ti 3d_xy orbitals when the thicknesses of LaAlO₃ and BaTiO₃ layers are over 4.5 unit cells. We have also revealed the interfacial electronic characteristics of the LaAlO₃/BaTiO₃ system, by showing the completely spin-polarized 2DEG mostly confined at the superlattice interface. The interfacial charge carrier mobility and conductivity are found to be converged beyond the critical thickness. Therefore, we can regulate the interfacial confinement for the spin-polarized 2DEG and quantum transport properties in LaAlO₃/BaTiO₃ superlattice via controlling the thicknesses of the LaAlO₃ and BaTiO₃ layers.