2015/05/15 by Se Young Park, Andrew J. Millis, Park, Se Young +1
Chemical Engineering · Chemistry · Materials Science · #Advanced Physical and Chemical Molecular Interactions #Catalysis and Oxidation Reactions #Electronic and Structural Properties of Oxides #FOS: Physical sciences #Strongly Correlated Electrons (cond-mat.str-el)
paper · pdf · doi:10.48550/arxiv.1505.04183
openalex publication_date 2015/05/15 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The density functional plus U method is used to obtain the electronic structure, lattice relaxation and metal-insulator phase diagram of superlattices consisting of m layers of Gadolinium Titanate (GdTiO3) alternating with n layers of Strontium Titanate (SrTiO3). Metallic phases occur when the number of SrTiO3 layers is large or the interaction U is small. In metallic phases, the mobile electrons are found in the SrTiO3 layers, with near-interface electrons occupying xy-derived bands, while away from the interface the majority of electrons reside in xz/yz bands. As the thickness of the SrTiO3 layers decreases or the on-site interaction U increases a metal-insulator transition occurs. Two different insulating states are found. When the number of SrTiO3 layers is larger than one, we find an insulating state with two sublattice charge and orbital ordering and associated Ti-O bond length disproportionations. When the number of SrTiO3 units per layer is one, a different insulating phase occurs driven by orbital ordering within the quasi one-dimensional xz/yz bonding bands connecting Ti atoms across the SrO layer. In this phase there is no sublattice charge ordering or bond disproportionation. The critical U for the single-layer insulator is ∼ 2.5 eV, much less than critical U ∼ 3.5 eV required to drive the metal-insulator transition when the number of SrTiO3 is larger than one. Inconsistencies between the calculation and the experiment suggest that many-body correlations may be important. A local inversion symmetry breaking around Ti atoms suggests the possibility of in-plane ferroelectric polarization in the insulating phase.