Epitaxy of hexagonal ABO$_3$ quantum materials

TL;DR

This review discusses the epitaxial growth of hexagonal ABO3 quantum materials, highlighting their unique properties, stability, and potential for discovering new phenomena like high-temperature superconductivity and topological phases.

Contribution

It provides a comprehensive overview of thin film stabilization, substrate templating, and the potential to realize metastable hexagonal oxides with novel quantum properties.

Findings

Hexagonal ABO3 oxides exhibit distinct quantum phenomena from cubic perovskites.

Thin film techniques enable stabilization of metastable hexagonal phases.

Potential for discovering high-temperature superconductivity and topological phases.

Abstract

Hexagonal $AB$O$_3$ oxides ($A$, $B$ = cation) are a rich materials class for realizing novel quantum phenomena. Their hexagonal symmetry, oxygen trigonal bipyramid coordination and quasi-two dimensional layering give rise to properties distinct from those of the cubic $AB$O$_3$ perovskites. As bulk materials, most of the focus in this materials class has been on the rare earth manganites, $R$MnO$_3$ ($R$ = rare earth); these materials display coupled ferroelectricity and antiferromagnetic order. In this review, we focus on the thin film manifestations of the hexagonal $AB$O$_3$ oxides. We cover the stability of the hexagonal oxides and substrates which can be used to template the hexagonal structure. We show how the thin film geometry not only allows for further tuning of the bulk-stable manganites but also the realization of metastable hexagonal oxides such as the $R$FeO$_3$ that combine ferroelectricity with weak ferromagnetic order. The thin film geometry is a promising platform to stabilize additional metastable hexagonal oxides to search for predicted high-temperature superconductivity and topological phases in this materials class.