Electrostatic carrier doping of GdTiO$_{3}$/SrTiO$_{3}$ heterostructures

Two-dimensional electron gases (2DEGs) at interfaces between Mott insulators and band insulators have attracted significant attention because they can exhibit unique properties, such as strong electron correlations, superconductivity and magnetism. At interfaces between SrTiO$_{3}$ and the rare earth titanates (Mott insulators) an interfacial fixed polar charge arises due to a polarization discontinuity, which can be compensated by a 2DEG, residing in the bands of the Mott/band insulator. In this presentation, we report on intrinsic electronic reconstructions at a Mott/band insulator interface between stoichiometric GdTiO$_{3}$ and SrTiO$_{3}$ that were grown using molecular beam epitaxy. The sheet carrier densities of all GdTiO$_{3}$/SrTiO$_{3}$ heterostructures containing more than one unit cell of SrTiO$_{3}$ are approximately 1/2 electron per unit cell, independent of layer thickness and growth sequence. These carrier densities closely meet the electrostatic requirements for compensating the fixed charge at these polar interfaces. Based on the experimental measurements, insights into the location and confinement of the charge and the influence of different electrostatic boundary conditions are obtained.