Epitaxial stabilization of SrCu$_3$O$_4$ with infinite Cu$_{3/2}$O$_2$ layers

TL;DR

This paper reports the synthesis and characterization of a novel metastable SrCu₃O₄ thin film with infinite Cu₃O₄ layers, revealing its potential as a parent material for electron-doped superconductivity.

Contribution

It demonstrates the epitaxial growth of SrCu₃O₄ with infinite Cu₃O₄ layers and provides insights into its electronic structure and stability.

Findings

SrCu₃O₄ is a metastable phase stabilized by tensile strain.

The material exhibits insulating behavior consistent with Cu²⁺ valence.

First-principles calculations show stabilization of unoccupied $d_{3z^2-r^2}$ band.

Abstract

We report the epitaxial thin film synthesis of SrCu$_3$O$_4$ with infinitely stacked Cu$_3$O$_4$ layers composed of edge-sharing CuO$_4$ square-planes, using molecular beam epitaxy. Experimental and theoretical characterizations showed that this material is a metastable phase that can exist by applying tensile biaxial strain from the (001)-SrTiO$_3$ substrate. SrCu$_3$O$_4$ shows an insulating electrical resistivity in accordance with the Cu$^{2+}$ valence state revealed X-ray photoelectron spectroscopy. First-principles calculations also indicated that the unoccupied $d_{3z^2-r^2}$ band becomes substantially stabilized owing to the absence of apical anions, in contrast to $A_2$Cu$_3$O$_4$Cl$_2$ ($A = $Sr, Ba) with an $A_2$Cl$_2$ block layer and therefore a trans-CuO$_4$Cl$_2$ octahedron. These results suggest that SrCu$_3$O$_4$ is a suitable parent material for electron-doped superconductivity based on the Cu$_3$O$_4$ plane.