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Tunable Transport Dimensionality of Electrons in Mott- and Band-insulator LaTiO3/SrTiO3 Superlattices

Jeong Ho You (Southern Methodist University), Jun Hee Lee (Department of Physics and Astronomy, Rutgers University)

Synthesis, Characterization, and Modeling of Low-Dimensional Nanomaterials

Wed 9:00 - 10:30

Salomon 202

Transport dimensionality of electron in LaTiO3/SrTiO3 superlattice has been investigated using the Density Functional Theory calculations with LSDA + U method. SrTiO3 is a band insulator with an empty 3d0 state, while LaTiO3 is a Mott insulator with an occupied 3d1 state. When SrTiO3 and LaTiO3 are adjoined to form a heterostructure, the 3d1 electron in LaTiO3 spreads over SrTiO3 layers by filling the empty 3d0 state which contributes to the conductivity. Different distribution trends between dxy and dyz/dzx electrons have been observed. The dxy electron is highly localized at the interface due to the LaO-induced potential, while dyz/dzx electron is almost homogeneously distributed over the entire structure. The Ti atom-resolved projected dxy density of state has revealed the quantum-well-like step increments which appears as flat bands along Z direction in bandstructures. For three unit cells or thicker SrTiO3 layers, there are two lowest dxy flat bands which correspond to two step-like increments in density of state at Ti atom at the interface. Electrons occupying these two low-energy bands can transport only along the interface, but not normal to the interface, which confirms the formation of two dimensional electron gas at the interface. These low-energy dxy bands remain the same for three u.c. or thicker SrTiO3 layers, which indicates the change of dimensionality of major carriers from three- to two-dimension at three unit cell of SrTiO3 layers.