Infinite-layer Oxide Research Articles

Tuning magnetic anisotropy and Dzyaloshinskii-Moriya interaction via interface engineering in nonisostructural SrCuO2/SrRuO3 heterostructures

We report a theoretical investigation on the effects of interface reconstruction on magnetic anisotropy (MA) and Dzyaloshinskii-Moriya interaction (DMI) for nonisostructural heterostructures formed by an infinite-layer oxide ${\mathrm{SrCuO}}_{2}$ and a perovskite oxide ${\mathrm{SrRuO}}_{3}$. Due to the atomic, charge, spin, and orbital reconstructions at interface, the SRO film thickness-dependent magnetic anisotropy oscillation behavior has been greatly tuned in two ${\mathrm{SrCuO}}_{2}/{\mathrm{SrRuO}}_{3}$ heterostructures. A strong DMI of 3.5 meV/Ru and a large DMI/exchange constant ratio $|D/J|$ of 0.63 are obtained at the ${\mathrm{CuO}}_{2}\text{\ensuremath{-}}\mathrm{Sr}\text{\ensuremath{-}}{\mathrm{RuO}}_{2}$ interface, which are beneficial to the creation and stability of skyrmions. Besides, the DMI is tunable, monotonically decreasing with the increase of the content of the apical oxygen ions in the interfacial layer, and takes the minimal value of 0.1 meV/Ru at the ${\mathrm{CuO}}_{2}\text{\ensuremath{-}}\mathrm{SrO}\text{\ensuremath{-}}{\mathrm{RuO}}_{2}$ interface. We evaluate the formation energy of oxygen vacancy in interface SRO layer, which turns out to be half as much as that in bulk SRO. This small value ensures the experimental feasibility towards two interfaces. Combining first-principles calculations with tight-binding model, we find that the effectively modulated MA and DMI at the ${\mathrm{CuO}}_{2}\text{\ensuremath{-}}\mathrm{Sr}\text{\ensuremath{-}}{\mathrm{RuO}}_{2}$ interface are mainly associated with the occupation of ${d}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ orbital, the enhanced interface symmetry breaking, and orbital hybridization. The present work demonstrates the distinct features of the interface formed between nonisostructural oxides and suggests a conceptually different strategy towards the modulation of MA and DMI.

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 (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.

Structural and electronic properties ofSrFeO2from first principles

We report on a first-principles study of ${\text{SrFeO}}_{2}$, an infinite-layer oxide with Fe atoms in a perfect square-planar coordination down to essentially 0 K. Our results reveal that this striking behavior relies on the double occupation of the $3{d}_{{z}^{2}}$ orbitals of high-spin ${\text{Fe}}^{2+}$. Such an electronic state results from electrostatic and hybridization effects, the latter enabling a large reduction in the intra-atomic exchange splitting of the ${z}^{2}$ electrons.