Dresden 2009 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 33: Methods: Electronic structure theory II

O 33.3: Vortrag

Mittwoch, 25. März 2009, 11:00–11:15, SCH A316

Tailoring the electronic properties of LaAlO₃ films on SrTiO₃(001) via a SrTiO₃-capping layer — •Katrin Otte¹, Rossitza Pentcheva¹, and Warren E. Pickett² — ¹Section Crystallography, Dept. of Earth and Environmental Sciences, University of Munich — ²Department of Physics, UC Davis

The two-dimensional electron gas emerging at the LaAlO₃(LAO)/ SrTiO₃(STO) interface [1] is an example of the novel electronic states that can be realized in heterostructures of a polar and a nonpolar band insulator. Recently, Thiel et al. [2] reported a critical thickness of four monolayers (MLs) beyond which the interface of LAO-films on a STO(001) substrate becomes conducting. Using density functional theory (DFT) calculations we demonstrate here that an STO-capping layer can trigger the insulator-to-metal transition already at two MLs of LAO. We have varied both the number of LAO and STO-capping layers and find that already the first STO-capping layer reduces the band gap by 1.2 eV, while additional layers only have a small impact. We identify O2p surface states of alternating p_x, p_y-character as the origin for the band gap collapse. Structural optimization indicates that the lattice polarization in the STO-capping layer has opposite sign to the LAO film.

Altogether, an STO-capping layer represents an alternative pathway to tune the electronic properties of the system with potential for future device applications.

[1] A.Ohtomo and H.Y.Hwang, Nature 427, 423 (2004)

[2] S.Thiel et al., Science 313, 1942 (2006)