Reticcioli Michele, Wang Zhichang, Schmid Michael, Wrana Dominik, Boatner Lynn A, Diebold Ulrike, Setvin Martin, Franchini Cesare
University of Vienna, Faculty of Physics, Center for Computational Materials Science, Vienna, Austria.
Institute of Applied Physics, Technische Universität Wien, Vienna, Austria.
Nat Commun. 2022 Jul 25;13(1):4311. doi: 10.1038/s41467-022-31953-6.
Excess charge on polar surfaces of ionic compounds is commonly described by the two-dimensional electron gas (2DEG) model, a homogeneous distribution of charge, spatially-confined in a few atomic layers. Here, by combining scanning probe microscopy with density functional theory calculations, we show that excess charge on the polar TaO termination of KTaO(001) forms more complex electronic states with different degrees of spatial and electronic localization: charge density waves (CDW) coexist with strongly-localized electron polarons and bipolarons. These surface electronic reconstructions, originating from the combined action of electron-lattice interaction and electronic correlation, are energetically more favorable than the 2DEG solution. They exhibit distinct spectroscopy signals and impact on the surface properties, as manifested by a local suppression of ferroelectric distortions.
离子化合物极性表面上的过量电荷通常用二维电子气（2DEG）模型来描述，即电荷的均匀分布，在几个原子层的空间范围内受到限制。在这里，通过将扫描探针显微镜与密度泛函理论计算相结合，我们表明，KTaO(001)的极性TaO端面上的过量电荷形成了具有不同程度空间和电子局域化的更复杂电子态：电荷密度波（CDW）与强局域化的电子极化子和双极化子共存。这些表面电子重构源于电子-晶格相互作用和电子关联的联合作用，在能量上比2DEG解决方案更有利。它们表现出独特的光谱信号并对表面性质产生影响，如铁电畸变的局部抑制所示。
