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Arras, Remi; Ruiz, Victor G.; Pickett, Warren E.; Pentcheva, Rossitza (2012): Tuning the two-dimensional electron gas at the LaAlO3/SrTiO3(001) interface by metallic contacts. In: Physical Review B, Vol. 85, Nr. 12
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Abstract

Density functional theory (DFT) calculations reveal that adding ametallic overlayer on LaAlO3/SrTiO3(001) alters significantly theelectric field within the polar LaAlO3 film. For Al or Ti metal contactsthe electric field is eliminated, leading to a suppression of thethickness-dependent insulator-to-metal transition observed in uncoveredfilms. Independent of the LaAlO3 thickness, both the surface and theinterface are metallic, with an enhanced carrier density at theinterface relative to LaAlO3/SrTiO3(001) after the metallizationtransition. Monolayer thick contacts of Ti develop a finite magneticmoment and for a thin SrTiO3 substrate induce a spin-polarizedtwo-dimensional electron gas at the n-type interface, due to confinementeffects in the SrTiO3 slab. For transition (Fe, Co, Pt) and noble metalcontacts (Cu, Ag, Au) a finite and even enhanced (Au) internal electricfield develops within LaAlO3. Results for a representative series ofmetallic overlayers on LaAlO3/SrTiO3(001) (Na, Al; Ti, Fe, Co, Pt; Cu,Ag, Au) reveal broad variation of band alignment, size of Schottkybarrier, carrier concentration and lattice polarization at theLaAlO3/SrTiO3(001) interface. The identified relationship to the size ofwork function of the metal on LaAlO3 provides guidelines on how thecarrier density at the LaAlO3/SrTiO3 interface can be controlled by thechoice of the metal contact.