National High Magnetic Field Laboratory, Department of Physics, Florida State University, Tallahassee, Florida 32310, USA.
Nat Commun. 2013;4:2351. doi: 10.1038/ncomms3351.
Emergent phenomena, including superconductivity and magnetism, found in the two-dimensional electron liquid (2-DEL) at the interface between the insulators lanthanum aluminate (LaAlO3) and strontium titanate (SrTiO3) distinguish this rich system from conventional 2D electron gases at compound semiconductor interfaces. The origin of this 2-DEL, however, is highly debated, with focus on the role of defects in the SrTiO3, while the LaAlO3 has been assumed perfect. Here we demonstrate, through experiments and first-principle calculations, that the cation stoichiometry of the nominal LaAlO3 layer is key to 2-DEL formation: only Al-rich LaAlO3 results in a 2-DEL. Although extrinsic defects, including oxygen deficiency, are known to render LaAlO3/SrTiO3 samples conducting, our results show that in the absence of such extrinsic defects an interface 2-DEL can form. Its origin is consistent with an intrinsic electronic reconstruction occurring to counteract a polarization catastrophe. This work provides insight for identifying other interfaces where emergent behaviours await discovery.
在绝缘体镧铝氧化物 (LaAlO3) 和钛酸锶 (SrTiO3) 之间的界面处的二维电子液体 (2-DEL) 中发现的紧急现象，包括超导性和磁性，使这个丰富的系统有别于传统的化合物半导体界面处的二维电子气体。然而，这个 2-DEL 的起源存在很大争议，焦点在于 SrTiO3 中缺陷的作用，而 LaAlO3 则被认为是完美的。在这里，我们通过实验和第一性原理计算证明，名义上的 LaAlO3 层的阳离子化学计量比对于 2-DEL 的形成是关键的：只有富 Al 的 LaAlO3 才会导致 2-DEL。尽管众所周知，包括氧空位在内的外在缺陷会使 LaAlO3/SrTiO3 样品具有导电性，但我们的结果表明，在没有这种外在缺陷的情况下，界面 2-DEL 也可以形成。其起源与一种内在的电子重构一致，这种重构是为了抵消极化灾难。这项工作为识别其他有待发现的紧急行为的界面提供了见解。
