Available on-demand - F.MT03.06.02
Identifying High-Temperature Superconductivity at Complex Oxide Interfaces
Y. Eren Suyolcu1,2,Gennady Logvenov1,Peter van Aken1
Max Planck Institute for Solid State Research1,Cornell University2
Transition metal oxide heterostructures host many novel functionalities and have stimulated large interest due to the possibilities of tailoring the functionalities at the atomic layer scale. It is the complex interactions at the interfaces of epitaxial oxide systems that contribute to intriguing physical effects induced by the local variation of electronic and ionic species. In this work, we focus on high-temperature superconductivity (HTSC) of La2CuO4-based iso-structural and non–iso-structural systems. In particular, we fabricate (i) La1.6A0.4CuO4–La2CuO4 (A = Ca, Sr, Ba) metallic–insulating (M–I) bilayers  and (ii) (La,Sr)2CuO4–SrMnO3–LaMnO3–La2CuO4 multilayers  using atomic-layer-by layer oxide molecular beam epitaxy (ALL-Oxide MBE) .
In order to correlate local structure and superconducting properties, we extensively probe the interfaces using aberration-corrected analytical scanning transmission electron microscopy (STEM) techniques including high-angle annular dark-field (HAADF) and annular bright-field (ABF) imaging, electron energy-loss spectroscopy (EELS), and energy-dispersive X-ray spectroscopy (EDXS). For the atomic-resolution analyses, a JEOL JEM-ARM200F STEM equipped with a cold field-emission electron source, a probe Cs-corrector (DCOR, CEOS GmbH), a Gatan GIF Quantum ERS spectrometer and a large solid-angle JEOL Centurio SDD-type EDXS detector was used. STEM imaging and EELS were performed at probe semi-convergence angles of 20 mrad and 28 mrad, respectively. The collection angles for HAADF and ABF images were 75-310 mrad and 11-23 mrad, respectively. O-O picker tool  software has been utilized for STEM image quantification.
The choice of the dopant substantially influences the superconducting mechanisms as a consequence of the dopant distribution near the nominal M–I bilayers interfaces. In the case of Sr- and Ca-doping, sharp interfaces induce striking interface effects, i.e. electronic redistribution. Differently, for Ba-doped bilayer, HTSC is attributed to “classical” homogeneous doping determined by cationic intermixing. Moreover, we demonstrate that sharper Sr-doped La2CuO4 interfaces can be achieved by the heteroepitaxial contacts with manganite layers. The dopant distribution in La2CuO4 is affected by the elemental intermixing at the first atomic monolayer of the interfacial LaMnO3 contact. Different superconducting behavior (interface vs filamentary) at the two different interface systems are correlated with the interface sharpness and will be discussed in detail.
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