2D superconductidy driven by interfacial electron-phonon coupling at the BaPbO$_3$/BaBiO$_3$ bilayer

TL;DR

This study uses first-principles calculations to explore the electronic and structural properties of the BaPbO$_3$/BaBiO$_3$ bilayer, revealing interfacial electron-phonon coupling as a key factor in 2D superconductivity.

Contribution

It demonstrates how interfacial electron-phonon interactions induce 2D superconductivity in the BaPbO$_3$/BaBiO$_3$ heterostructure, highlighting the role of charge transfer and specific carrier types.

Findings

Preservation of bulk-like properties in BBO's inner layers.

Partial breaking of breathing distortions at the interface.

Electron-phonon coupling explains the observed critical temperature.

Abstract

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.