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Direct imaging of the electron liquid at oxide interfaces
Song, Kyung,Ryu, Sangwoo,Lee, Hyungwoo,Paudel, Tula R.,Koch, Christoph T.,Park, Bumsu,Lee, Ja Kyung,Choi, Si-Young,Kim, Young-Min,Kim, Jong Chan,Jeong, Hu Young,Rzchowski, Mark S.,Tsymbal, Evgeny Y.,E Nature Publishing Group UK 2018 Nature nanotechnology Vol.13 No.3
<P>The breaking of symmetry across an oxide heterostructure causes the electronic orbitals to be reconstructed at the interface into energy states that are different from their bulk counterparts(1). The detailed nature of the orbital reconstruction critically affects the spatial confinement and the physical properties of the electrons occupying the interfacial orbitals(2-4). Using an example of two-dimensional electron liquids forming at LaAlO3/SrTiO3 interfaces(5,6) with different crystal symmetry, we show that the selective orbital occupation and spatial quantum confinement of electrons can be resolved with subnanometre resolution using inline electron holography. For the standard (001) interface, the charge density map obtained by inline electron holography shows that the two-dimensional electron liquid is confined to the interface with narrow spatial extension (similar to 1.0 +/- 0.3 nm in the half width). On the other hand, the two-dimensional electron liquid formed at the (111) interface shows a much broader spatial extension (similar to 3.3 +/- 0.3 nm) with the maximum density located similar to 2.4 nm away from the interface, in excellent agreement with density functional theory calculations.</P>
Publisher Correction: Direct imaging of the electron liquid at oxide interfaces
Song, Kyung,Ryu, Sangwoo,Lee, Hyungwoo,Paudel, Tula R.,Koch, Christoph T.,Park, Bumsu,Lee, Ja Kyung,Choi, Si-Young,Kim, Young-Min,Kim, Jong Chan,Jeong, Hu Young,Rzchowski, Mark S.,Tsymbal, Evgeny Y.,E Nature Publishing Group UK 2018 Nature nanotechnology Vol.13 No.7
In the version of this Letter originally published, in two instances in Fig. 1 the layers in the cross-sectional view of the (001) interface were incorrectly labelled: in Fig. 1b SrO<SUP>+</SUP> should have read SrO<SUP>0</SUP>; in Fig. 1c LaO<SUP>+</SUP>, AlO<SUB>2</SUB><SUP>–</SUP>, LaO<SUP>+</SUP>, TiO<SUB>2</SUB><SUP>0</SUP>, SrO<SUP>+</SUP>, TiO<SUB>2</SUB><SUP>0</SUP> should have read LaO<SUB>3</SUB><SUP>3–</SUP>, Al<SUP>3+</SUP>, LaO<SUB>3</SUB><SUP>3–</SUP>, Ti<SUP>4+</SUP>, SrO<SUB>3</SUB><SUP>4–</SUP>, Ti<SUP>4+</SUP>. In Fig. 3c the upper-right equation read –σ<SUB>s</SUB> = –e/2a<SUP>2</SUP> but should have read –σ<SUB>s</SUB> = e/2a<SUP>2</SUP> and in Fig. 3f the lower-right equation read –σ<SUB>s</SUB> = –e/2√3a<SUP>2</SUP> but should have read σ<SUB>s</SUB> = –e/2√3a<SUP>2</SUP>. These errors have now been corrected in the online version of the Letter.
Direct observation of a two-dimensional hole gas at oxide interfaces
Lee, H.,Campbell, N.,Lee, J.,Asel, T. J.,Paudel, T. R.,Zhou, H.,Lee, J. W.,Noesges, B.,Seo, J.,Park, B.,Brillson, L. J.,Oh, S. H.,Tsymbal, E. Y.,Rzchowski, M. S.,Eom, C. B. Nature Publishing Group UK 2018 Nature materials Vol.17 No.3
<P>The discovery of a two-dimensional electron gas (2DEG) at the LaAlO3/SrTiO3 interface(1) has resulted in the observation of many properties(2-5) not present in conventional semiconductor heterostructures, and so become a focal point for device applications(6-8). Its counterpart, the two-dimensional hole gas (2DHG), is expected to complement the 2DEG. However, although the 2DEG has been widely observed(9), the 2DHG has proved elusive. Herein we demonstrate a highly mobile 2DHG in epitaxially grown SrTiO3/LaAlO3/SrTiO3 heterostructures. Using electrical transport measurements and in-line electron holography, we provide direct evidence of a 2DHG that coexists with a 2DEG at complementary heterointerfaces in the same structure. First-principles calculations, coherent Bragg rod analysis and depth-resolved cathodoluminescence spectroscopy consistently support our finding that to eliminate ionic point defects is key to realizing a 2DHG. The coexistence of a 2DEG and a 2DHG in a single oxide heterostructure provides a platform for the exciting physics of confined electron-hole systems and for developing applications.</P>