It was shown that strong correlations in the oxygen 2p states might have to be assumed in order to account for the observed insulating behavior at charged (001)-interfaces between these band insulators. Using correlated band theory applied to the O 2p states, an insulating p-type interface was obtained only when a disproportionated charge- orbital- and spin-ordered oxygen Pπ magnetic hole was formed; centered between Al3+ ions in the AlO2 layer at the interface. An alternative explanation involved charge compensation by O vacancies that accommodated the holes as charge-conjugate F centers. For the n-type interface, a charge-disproportionated Ti4++Ti3+ layer was obtained with ferromagnetic alignment of the spins resulting from occupied dxy orbitals on checkerboard Ti3+ sites. Electron hopping on a 50%-occupied Ti sub-lattice (quarter-filled band) and/or lattice relaxations were considered as being the origin of the measured conductivity.

Charge Localization or Itineracy at LaAlO3/SrTiO3 Interfaces - Hole Polarons, Oxygen Vacancies, and Mobile Electrons. R.Pentcheva, W.E.Pickett: Physical Review B, 2006, 74[3], 035112 (7pp)