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

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 (SrCuO 2 /SrTiO 3 and SrCuO 2 /KTaO 3 ). 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 TiO 2 and CuO 2 interfacial layers, unlike LaAlO 3 /SrTiO 3 for which 2DEG exists only in the TiO 2 interfacial layer. More than that, no metal-to-insulator transition is observed as the SrCuO 2 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 SrCuO 2 /SrTiO 3 (KTaO 3 ) interface, the conducting states in the interface TiO 2 (TaO 2 ) layer follows the d x y < d 3 z 2 − r 2 < d x z / y z orbital order rather than the d xy < d xz / yz orbital order of paradigm LaAlO 3 /SrTiO 3 (KTaO 3 ), exhibiting enhanced interfacial conduction. This work suggests the great potential of heterointerfaces composed of non-isostructural oxides for fundamental research.