Two-dimensional superconductivity driven by interfacial electron-phonon coupling in a BaPbO3/BaBiO3 bilayer

Abstract

The recent discovery of two-dimensional (2D) superconductivity at the interface of BaPbO3 (BPO) and BaBiO3 (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 behavior 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 three-dimensional-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 below 3.5 K. We hope these findings will motivate future research to explore different interfaces with charge-ordered semiconductors such as BBO in order to trigger this fascinating 2D behavior.