金属覆盖的（111）LaAlO3/SrTiO3界面导电性和超导电性的共存
Concomitant appearance of conductivity and superconductivity in (111)LaAlO3/SrTiO3 interface with metal capping
摘要：
在极性氧化物界面中，需要一定数量的单层（ML）才能出现导电性。电导率的这个阈值是通过积累足够的电势来启动电荷转移到界面来解释的。在这里，我们研究的实验和理论的（111）SrTiO 3/LaAlO 3界面的临界厚度，tc，九个外延LaAlO 3 ML是需要把界面从绝缘到导电，甚至超导。我们发现，TC降低到3 ML时，沉积钴覆盖层（盖帽）和6 ML铂盖帽。后一结果与（100）界面形成对比，其中铂覆盖使tc增加超过裸界面。我们的密度泛函理论计算证实了所观察到的裸露和金属覆盖的界面的电导率阈值。有趣的是，对于（111）SrTiO 3/LaAlO 3/Metal界面，导电性与超导性相伴出现，而（100）SrTiO 3/LaAlO 3/Metal界面的tc小于超导临界厚度。我们将这种差异归因于（111）界面的e 'g与（001）界面的dxy的不同轨道极化。
英文摘要：
In polar-oxide interfaces, a certain number of monolayers (ML) is needed for conductivity to appear. This threshold for conductivity is explained by accumulating sufficient electric potential to initiate charge transfer to the interface. Here we study experimentally and theoretically the (111) SrTiO3/LaAlO3 interface where a critical thickness, tc, of nine epitaxial LaAlO3 ML is required to turn the interface from insulating to conducting and even superconducting. We show that tc decreases to 3ML when depositing a cobalt over-layer (capping) and 6ML for platinum capping. The latter result contrasts with the (100) interface, where platinum capping increases tc beyond the bare interface. The observed threshold for conductivity for the bare and the metal-capped interfaces is confirmed by our density functional theory calculations. Interestingly, for (111) SrTiO3/LaAlO3/Metal interfaces, conductivity appears concomitantly with superconductivity in contrast with the (100) SrTiO3/LaAlO3/Metal interfaces where tc is smaller than the critical thickness for superconductivity. We attribute this dissimilarity to the different orbital polarization of e'g for the (111) versus dxy for the (001) interface.
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