K-doped Ba122 epitaxial thin film on MgO substrate by buffer engineering

TL;DR

This paper reports the successful molecular beam epitaxy growth of K-doped Ba122 superconducting thin films on MgO substrates, achieving high critical temperature and current density, enabling further grain boundary studies.

Contribution

It demonstrates the use of undoped Ba122 as a buffer layer for epitaxial growth of K-doped Ba122 on MgO, a novel approach for this material system.

Findings

Critical temperature of 39.8 K achieved

Critical current density of 3.9 MA/cm² at 4 K

Epitaxial growth enabled for grain boundary studies

Abstract

Molecular beam epitaxy of K-doped Ba122 (Ba$_{1-x}$K$_x$Fe$_\text{2}$As$_\text{2}$) superconductor was realized on a MgO substrate. Microstructural observation revealed that the undoped Ba122 served as a perfect buffer layer for epitaxial growth of the K-doped Ba122. The film exhibited a high critical temperature of 39.8 K and a high critical current density of 3.9 MA/cm$^\text{2}$ at 4 K. The successful growth of epitaxial thin film will enable artificial single grain boundary on oxide bicrystal substrates and reveal the grain boundary transport nature of K-doped Ba122.