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Pentcheva, Rossitza; Pickett, Warren E. (2009): Avoiding the Polarization Catastrophe in LaAlO3 Overlayers on SrTiO3(001) through Polar Distortion. In: Physical Review Letters, Vol. 102, No. 10
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A pronounced uniform polar distortion extending over several unit cellsenables thin LaAlO3 overlayers on SrTiO3(001) to counteract the chargedipole and thereby neutralize the “polarization catastrophe” that issuggested by simple ion counting. This unanticipated mechanism, obtainedfrom density functional theory calculations, allows several unit cellsof the LaAlO3 overlayer to remain insulating (hence, fully ionic). Theband gap of the system, defined by occupied O 2p states at the surfaceand unoccupied Ti 3d states at the interface in some cases similar to 20A distant, decreases with increasing thickness of the LaAlO3 film beforean insulator-to-metal transition and a crossover to an electronicreconstruction occurs at around five monolayers of LaAlO3.