Controlling the density of the two-dimensional electron gas at the SrTiO3/LaAlO3 interface

The polar discontinuity at the SrTiO3/LaAlO3 interface (STO/LAO) can in principle sustain an electron density of 3.3 x 10(14) cm(-2) (0.5 electrons per unit cell). However, experimentally observed densities are more than an order of magnitude lower. Using a combination of first-principles and Schrodinger-Poisson simulations we show that the problem lies in the asymmetric nature of the structure, i.e., the inability to form a second LAO/STO interface that is a mirror image of the first, or to fully passivate the LAO surface. Our insights apply to oxide interfaces in general, explaining for instance why the SrTiO3/GdTiO3 interface has been found to exhibit the full density of 3.3 x 10(14) cm(-2). DOI: 10.1103/PhysRevB.86.241108