In-plane ordering of O vacancies in a high-Tc cuprate superconductor with compressed Cu-O octahedrons: a first-principles cluster expansion study

TL;DR

This study uses first-principles calculations and Monte Carlo simulations to predict the ordered arrangement of oxygen vacancies in a high-Tc cuprate superconductor, revealing stable vacancy patterns that may influence its superconducting properties.

Contribution

It provides a detailed structural prediction of oxygen vacancy ordering in Ba2CuO$_{4-\delta}$ using a combined computational approach, offering insights into its superconducting mechanism.

Findings

O vacancies prefer in-plane positions due to Jahn-Teller distortion.

Ordered vacancy patterns form 1D chains and two-leg ladders.

Vacancy order remains stable up to approximately 900 K.

Abstract

A recently discovered high-Tc cuprate superconductor Ba2CuO$_{4-\delta}$ exhibits exceptional Jahn-Teller distortion, wherein the CuO6 octahedrons are compressed along the c axis. As a consequence, the O vacancies prefer to reside in the CuO2 plane, but the exact structure is not known. By combining first-principles total energy calculation with the automated structure inversion method, the effective cluster interactions of O vacancies are mapped out. Around $\delta$=0.8, where the 73K superconductivity was observed experimentally, we predict that the ordered O vacancies slice the CuO2 plane into not only 1D chains and but also two-leg ladders. A Monte Carlo simulation is performed based on the effective cluster interaction model, showing that such an ordering pattern is stable up to ~900 K. Our results put forth a concrete structural basis to discuss the underlying superconducting mechanism.