We report the observation of a two-dimensional electron system (2DES) at the $(110)$ surface of the transparent bulk insulator SnO${}_2$, and the tunability of its carrier density by means of temperature or Eu deposition. The 2DES is insensitive to surface reconstructions and, surprisingly, it survives even after exposure to ambient conditions –an extraordinary fact recalling the well known catalytic properties SnO${}_2$. Our data show that surface oxygen vacancies are at the origin of such 2DES, providing key information about the long-debated origin of $n$-type conductivity in SnO${}_2$, at the basis of a wide range of applications. Furthermore, our study shows that the emergence of a 2DES in a given oxide depends on a delicate interplay between its crystal structure and the orbital character of its conduction band.

中文翻译：

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SnO2（110）表面的可调谐二维电子系统

我们报告了在二维电子系统（2DES）的观测 $（110）$ 透明块状绝缘子SnO的表面${}_2$，以及通过温度或Eu沉积获得的载流子密度的可调性。2DES对表面重建不敏感，而且令人惊讶的是，即使暴露在环境条件下，它也能幸存下来–这是一个非凡的事实，让人想起了众所周知的催化性能SnO${}_2$。我们的数据表明，表面氧空位是此类2DES的起源，提供了有关长期争论的起源的关键信息。$ñ$SnO型电导率${}_2$，在广泛的应用基础上。此外，我们的研究表明，给定氧化物中2DES的出现取决于其晶体结构与导带轨道特性之间的微妙相互作用。