Epitaxial Stabilization of SrCu₃O₄ with Infinite\nCu_3/2O₂ Layers

Abstract

We\nreport the epitaxial thin-film synthesis of SrCu₃O₄ with infinitely stacked Cu₃O₄ layers\ncomposed of edge-sharing CuO₄ square planes, using\nmolecular-beam epitaxy. Experimental and theoretical characterizations\nshowed that this material is a metastable phase that can exist by\napplying tensile biaxial strain from the (001)-SrTiO₃ substrate.\nSrCu₃O₄ shows an insulating electrical resistivity\nin accordance with the Cu²⁺ valence state revealed by X-ray\nphotoelectron spectroscopy. First-principles calculations also indicated\nthat the unoccupied d_{3<i>z</i>²–<i>r</i>²} band becomes substantially stabilized\nowing to the absence of apical anions, in contrast to A₂Cu₃O₄Cl₂ (A = Sr, Ba) with an A₂Cl₂ block layer and therefore a <i>trans</i>-CuO₄Cl₂ octahedron. These results suggest\nthat SrCu₃O₄ is a suitable parent material for\nelectron-doped superconductivity based on the Cu₃O₄ plane.