Atomic Stripe Formation in Infinite-Layer Cuprates.

Abstract

High-temperature superconductivity appears in cuprate materials that have been tuned in a way where the copper–oxygen bond configuration and coordination is in a state of minimal energy. In competition with the Jahn–Teller effect, which impedes the formation of infinitely connected CuO2 planes, the state of minimal energy persists for planar copper–oxygen bond length variations of up to 10%. We have synthesized the infinite-layer phases of CaCuO2 and SrCuO2 as single-crystalline films using molecular beam epitaxy and performed in-plane scanning transmission electron microscopy mapping. For the infinite-layer phase of CaCuO2 with a short Cu–O bond length, the CuO2 planes maintain their minimal energy by forming distinguished atomic stripes. In contrast, atomic stripe formation does not occur in the infinite-layer phase of SrCuO2, which has a larger Cu–O bond length. The polar field provided by the charge reservoir layer in cuprates with infinitely connected CuO2 planes holds the key over the emergence of superconductivity and is vital to maintain infinitely connected CuO2 planes themselves.