Electric field-induced oxygen vacancies in YBa2Cu3O7

TL;DR

This study uses density-functional theory to explore how electric fields induce oxygen vacancies in YBa2Cu3O7, revealing vacancy migration mechanisms and screening effects relevant to its superconducting properties.

Contribution

It provides a detailed theoretical analysis of electric field effects on oxygen vacancy formation and migration in YBa2Cu3O7, advancing understanding of doping mechanisms in high-temperature superconductors.

Findings

Electric fields can extract oxygen atoms from CuO chains.

Vacancies tend to accumulate at the surface, favoring chain interior migration.

Electric field screening occurs near the surface, minimally affecting diffusion barriers.

Abstract

The microscopic doping mechanism behind the superconductor-to-insulator transition of a thin film of YBa2Cu3O7 was recently identified as due to the migration of O atoms from the CuO chains of the film. Here we employ density-functional theory calculations to study the evolution of the electronic structure of a slab of YBa2 Cu3 O7 in presence of oxygen vacancies under the influence of an external electric field. We find that under massive electric fields isolated O atoms are pulled out of the surface consisting of CuO chains. As vacancies accumulate at the surface, a configuration with vacancies located in the chains inside the slab becomes energetically preferred thus providing a driving force for O migration towards the surface. Regardless of the defect configuration studied, the electric field is always fully screened near the surface thus negligibly affecting diffusion barriers across the film.