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Band alignment at band-insulator/Mott-insulator interfaces



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Recent experiments have demonstrated the formation of a two-dimensional electron gas (2DEG) with a high density of 3 × 1014 cm–2 at the interface of a band insulator (SrTiO3) and a Mott insulator (GdTiO3), with potential application in electronic devices. This contrasted with the 2DEG at the SrTiO3/LaAlO3 interface, two band insulators, for which the reported electron densities are an order of magnitude lower. Understanding the differences between SrTiO3/LaAlO3 and SrTiO3/GdTiO3, and identifying other materials combinations that also give rise to such high 2DEG densities will add flexibility to materials design and contribute to advancing this field of research. Based on first-principles calculations, we propose that YTiO3 combined with SrTiO3 will also lead to a 2DEG with density of 3 × 1014 cm–2. YTiO3 is a Mott insulator, with lattice parameters and band structure similar to those of GdTiO3. We calculate the band alignment at the SrTiO3/YTiO3 interface, compare with the SrTiO3/GdTiO3 system, and discuss the origins of the differences between the rare-earth titanates and LaAlO3 regarding the 2DEG densities. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)