界面电子-声子耦合驱动的BaPbO $_3$ / BaBiO $_3$双层膜二维超导
2D superconductidy driven by interfacial electron-phonon coupling at the BaPbO$_3$/BaBiO$_3$ bilayer
摘要：
最近在BaPbO $_3$（BPO）和BaBiO $_3$（BBO）界面处发现的二维超导电性促使我们通过第一性原理计算深入研究这种特殊异质结构中的电子和结构性质以及它们之间的关系。我们的研究结果表明，呼吸扭曲，电荷有序和半导体的行为，其本体形式的母体化合物BBO的特征，被保存在BPO/BBO双层的BBO侧的最内层。另一方面，在界面处，存在呼吸畸变的部分断裂，伴随着界面Bi离子和顶部BPO层之间的电荷转移。我们发现，两种类型的载流子共存于界面处，离域的3D像sp状态来自Pb离子和准2D的s状态从Bi的。我们得到了具有界面伸缩声子模的二维Bi态之间的电子-声子耦合和大的态密度，这可以解释实验观察到的低于3.5 K的临界温度。我们希望这些发现将激励未来的研究探索与电荷有序半导体BBO的不同界面，以触发这种迷人的2D行为。
英文摘要：
The recent discovery of 2D superconductivity at the interface of BaPbO$_3$ (BPO) and BaBiO$_3$ (BBO) has motivated us to study in depth the electronic and structural properties and the relation between them in this particular heterostructure, by means of first-principles calculations. Our results indicate that the breathing distortions, the charge ordering and the semiconducting behaviour that characterize the parent compound BBO in its bulk form, are preserved at the innermost layers of the BBO side of the BPO/BBO bilayer. On the other hand, at the interface, there is a partial breaking of the breathing distortions with a concomitant charge transfer between the interfacial Bi ions and the on top BPO layer. We show that two types of carriers coexist at the interface, the delocalized 3D like sp states coming from Pb ions and the quasi 2D s states from the Bi ones. We obtain a substantial electron-phonon coupling between the 2D Bi states with the interfacial stretching phonon mode and a large density of states that can explain the critical temperature experimentally observed bellow 3.5 K. We hope these findings will motivate future research to explore different interfaces with charge ordered semiconductors as BBO in order to trigger this fascinating 2D behavior.
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