A promising route to tailoring the electronic properties of quantum materials and devices rests on the idea of orbital engineering in multilayered oxide heterostructures. Here we show that the interplay of interlayer charge imbalance and ligand distortions provides a knob for tuning the sequence of electronic levels even in intrinsically stacked oxides. We resolve in this regard the $d$-level structure of layered Sr$_2$IrO$_4$ by electron spin resonance. While canonical ligand-field theory predicts $g_{\parallel}$-factors $\!<\!2$ for positive tetragonal distortions as present in Sr$_2$IrO$_4$, the experiment indicates $g_{\parallel}\!>\!2$. This implies that the iridium $d$ levels are inverted with respect to their normal ordering. State-of-the-art electronic-structure calculations confirm the level switching in Sr$_2$IrO$_4$, whereas we find them in Ba$_2$IrO$_4$ to be instead normally ordered. Given the nonpolar character of the metal-oxygen layers, our findings highlight the tetravalent transition-metal 214 oxides as ideal platforms to explore $d$-orbital reconstruction in the context of oxide electronics.

翻译：量子材料和装置电子特性的定制有希望的路径。 量子材料和装置电子特性的一个很有希望的路线在于多层氧化物结构中的轨道工程理念。 我们在这里显示, 跨层电荷不平衡和螺旋扭曲的相互作用为调整电子水平的顺序提供了一小节, 即使是在内在的堆叠氧化物中也是如此。 我们在这方面通过电子旋转共振解决了层层Sr$_ 2美元 美元 4美元 的等级结构。 虽然卡尼利根理论预测在多层氧化物结构中的轨道工程成本为$ $ ⁇ parall $ 。!!!!!......................................................................................................................................................................................