Intrinsic origin of the two-dimensional electron gas at polar oxide   interfaces
  The predictions of the polar catastrophe scenario to explain the occurrence of a metallic interface in heterostructures of the solid solution(LaAlO$_3$)$_{x}$(SrTiO$_3$)$_{1-x}$ (LASTO:x) grown on (001) SrTiO$_3$ were investigated as a function of film thickness and $x$. The films are insulating for the thinnest layers, but above a critical thickness, $t_c$, the interface exhibits a constant finite conductivity which depends in a predictable manner on $x$. It is shown that $t_c$ scales with the strength of the built-in electric field of the polar material, and is immediately understandable in terms of an electronic reconstruction at the nonpolar-polar interface. These results thus conclusively identify the polar-catastrophe model as the intrinsic origin of the doping at this polar oxide interface. 
M. L. Reinle-Schmitt, C. Cancellieri, D. Li, D. Fontaine, M. Medarde,   E. Pomjakushina, C. W. Schneider, S. Gariglio, Ph. G...
cond-mat.mtrl-sci