Two-dimensional conducting states in infinite-layer oxide/perovskite oxide hetero-structures

Abstract

Heterointerfaces sandwiched by oxides of dissimilar crystal structures will show strong interface reconstruction, leading to distinct interfacial effect arising from unusual physics. Here, we present a theoretical investigation on the interfaces between infinite-layer oxide and perovskite oxide (SrCuO2/SrTiO3 and SrCuO2/KTaO3). Surprisingly, we found well-defined two-dimensional electron gas (2DEG), stemming from atomic reconstruction and polar discontinuity at interface. Moreover, the 2DEG resides in both the TiO2 and CuO2 interfacial layers, unlike LaAlO3/SrTiO3 for which 2DEG exists only in the TiO2 interfacial layer. More than that, no metal-to-insulator transition is observed as the SrCuO2 layer thickness decreases to one unit cell, i.e., the metallicity of the new interface is robust. Further investigations show more unique features of the 2DEG. Due to the absence of apical oxygen at the SrCuO2/SrTiO3 (KTaO3) interface, the conducting states in the interface TiO2 (TaO2) layer follows the orbital order rather than the d xy < d xz/yz orbital order of paradigm LaAlO3/SrTiO3 (KTaO3), exhibiting enhanced interfacial conduction. This work suggests the great potential of heterointerfaces composed of non-isostructural oxides for fundamental research.