Figure 1

(Color online) Schematic picture of the structure showing the dependence of the electron distribution on the LAO layer thickness. It also shows how the La:STO thickness moves the La:STO/STO interface through this distribution allowing us to probe the distribution by changing the La:STO thickness.Reuse & Permissions

Figure 2

(Color online) Transport properties taken during cooling: (a) sheet resistance and (b) sheet carrier density of films with 10 ML La:STO and 4, 5, and 6 ML of ${\text{LaAlO}}_3$ on top. The inset in (a) shows the schematic layout of the samples and the inset in (b) shows an Arrhenius plot of the 5 ML LAO sample. (c) The solution for the potential from Poisson’s equation for samples with various LAO thicknesses and temperatures. For simplicity the La:STO and STO properties have been assumed to be the same. Assuming different properties will change the results quantitatively but qualitatively the trends remain the same. Thicker LAO layers allow the electrons to move further into the STO (here only shown at room temperature, at low temperature a similar effect is observed) but lowering the temperature (and increasing the dielectric constant) proves to be a much stronger effect.Reuse & Permissions

Figure 3

(Color online) A summary of the transport properties of samples with a constant LAO thickness of 5 ML and a variable La:STO thickness. In the top panel the residual resistance ratio is given together with the values for the sheet resistance at 300 and 20 K. In the bottom panel the number of carriers at 300 and 20 K are plotted as well as the mobility of the electrons at 20 K.Reuse & Permissions

Figure 4

(Color online) (a) The valence- and conduction-band arrangement for the three materials individually with the relevant parameters, where the dotted line is the Fermi level. (b) The reconstructed band picture after alignment of the Fermi level.Reuse & Permissions