Abstract
Transport dimensionality of Ti d electrons in (LaTiO sub(3)) sub(1) /(SrTiO sub(3)) sub(N) superlattices has been investigated using density functional theory with local spin-density approximation + U method. Different spatial distribution patterns have been found between Ti t sub(2)g orbital electrons. The d sub(xy) orbital electrons are highly localized near interfaces due to the potentials by positively charged LaO layers, while the degenerate d sub(yz) and d sub(xz) orbital electrons are more distributed inside SrTiO sub(3) insulators. For N > or = 3 unit cells (u.c.), the Ti d sub(xy) densities of state exhibit the staircaselike increments, which appear at the same energy levels as the d sub(xy) flat bands along the [top left corner]-Z direction in band structures. The k sub(z)-independent discrete energy levels indicate that the electrons in d sub(xy) flat bands are two-dimensional electron gases (2DEGs) which can transport along interfaces, but they cannot transport perpendicularly to interfaces due to the confinements in the potential wells by LaO layers. Unlike the d sub(xy) orbital electrons, the d sub(yz) and d sub(xz) orbital electrons have three-dimensional (3D) transport characteristics, regardless of SrTiO sub(3) thicknesses. The 2DEG formation by d sub(xy) orbital electrons, when N > or = 3 u.c., indicates the existence of critical SrTiO sub(3) thickness where the electron transport dimensionality starts to change from 3D to 2D in (LaTiO sub(3)) sub(1) /(SrTiO sub(3)) sub(N) superlattices.