The discovery of a two-dimensional electron system (2DES) at the interfaces of perovskite oxides such as $\mathrm{LaAl}{\mathrm{O}}_3$ and $\mathrm{SrTi}{\mathrm{O}}_3$ has motivated enormous efforts in engineering interfacial functionalities with this type of oxide heterostructures. However, the fundamental origins of the 2DES are still not understood, e.g., the microscopic mechanisms of coexisting interface conductivity and magnetism. Here we report a comprehensive spectroscopic investigation on the depth profile of 2DES-relevant $\mathrm{Ti}3d$ interface carriers using depth- and element-specific techniques like standing-wave excited photoemission and resonant inelastic scattering. We found that one type of Ti $3d$ interface carriers, which give rise to the 2DES are located within three unit cells from the n-type interface in the $\mathrm{SrTi}{\mathrm{O}}_3$ layer. Unexpectedly, another type of interface carriers, which are polarity-induced Ti-on-Al antisite defects, reside in the first three unit cells of the opposing $\mathrm{LaAl}{\mathrm{O}}_3$ layer (∼10 Å). Our findings provide a microscopic picture of how the localized and mobile Ti $3d$ interface carriers distribute across the interface and suggest that the 2DES and 2D magnetism at the $\mathrm{LaAl}{\mathrm{O}}_3/\mathrm{SrTi}{\mathrm{O}}_3$ interface have disparate explanations as originating from different types of interface carriers.

中文翻译：

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钙钛矿氧化物异质结构中的二维电子系统：极性诱导的取代缺陷的作用

在钙钛矿氧化物的界面上发现了二维电子系统（2DES），例如 $\mathrm{拉铝}{\mathrm{Ø}}_3$ 和 $\mathrm{锶钛}{\mathrm{Ø}}_3$这种类型的氧化物异质结构已经在工程界面功能方面做出了巨大的努力。但是，尚不了解2DES的基本起源，例如，界面电导率和磁性共存的微观机制。在这里，我们报告了有关2DES相关深度剖面的综合光谱研究$钛3d$使用特定于深度和元素的技术（例如驻波激发的光发射和共振非弹性散射）的界面载体。我们发现一种钛$3d$ 产生2DES的接口载体位于从 $\mathrm{锶钛}{\mathrm{Ø}}_3$层。出乎意料的是，另一种类型的界面载体，是极性诱导的Al-Ti上的对位缺陷，位于相对分子的前三个晶胞中$\mathrm{拉铝}{\mathrm{Ø}}_3$层（〜10Å）。我们的研究结果提供了有关局部和移动Ti的显微照片$3d$ 接口载流子分布在整个接口上，这表明在接口处的2DES和2D磁性 $\mathrm{拉铝}{\mathrm{Ø}}_3/\mathrm{锶钛}{\mathrm{Ø}}_3$ 接口具有不同的解释，因为它们来自不同类型的接口载体。