Abstract
Among the range of complex interactions, especially at the interfaces of epitaxial oxide systems, contributing to the occurrence of intriguing effects, a predominant role is played by the local structural parameters. In this study, oxide molecular beam epitaxy grown lanthanum cuprate-based bilayers (consisting of a metallic (M) and an insulating phase (I)), in which high-temperature superconductivity arises as a consequence of interface effects, are considered. With the aim of assessing the role of the dopant size on local crystal structure and chemistry, and on the interface functionalities, different dopants (Ca2+, Sr2+ and, Ba2+) are employed in the M-phase, and the M–I bilayers are investigated by complementary techniques, including spherical-aberration-corrected scanning transmission electron microscopy. A series of exciting outcomes are found: (i) the average out-of-plane lattice parameter of the bilayers is linearly dependent on the dopant ion size, (ii) each dopant redistributes at the interface with a characteristic diffusion length, and (iii) the superconductivity properties are highly dependent on the dopant of choice. Hence, this study highlights the profound impact of the dopant size and related interface chemistry on the functionalities of superconducting oxide systems.
Highlights
High-quality complex oxide heterostructures are excellent systems for studying interface phenomena arising from the interaction between neighboring layers[1, 2]
We investigated La1.6A0.4CuO4–La2CuO4 bilayers, which were grown by using the atomic-layer-by-layer oxide molecular beam epitaxy technique (ALL-oxide MBE)[30], by employing several and complementary experimental techniques: atomic force microscopy (AFM), X-ray diffraction (XRD), low-temperature direct current (DC) resistance measurements, magnetic susceptibility measurements and high-resolution scanning transmission electron microscopy (STEM)
The growth of each M–I bilayer was monitored by in-situ reflection high-energy electron diffraction (RHEED)
Summary
High-quality complex oxide heterostructures are excellent systems for studying interface phenomena arising from the interaction between neighboring layers[1, 2]. Depending on the choice of the constituents, different microscopic phenomena can occur at the interfaces, including e.g. electronic and orbital reconstruction, magnetic exchange interactions, crystal-structure distortions, chemical intermixing, or breaking of the crystal symmetry[3,4,5,6,7,8,9] In this context, one recent exciting finding was the observation by Gozar et al of high-temperature interface superconductivity (HT-IS) at the interface between epitaxially grown strontium-overdoped metallic (M) lanthanum cuprate (La1.55Sr0.45CuO4) and underdoped insulating (I) La2CuO4 (LCO) layers[10], none of which is superconducting if taken alone. The mismatch with the host La cation, whose ionic size is 121 pm, is −2.47%, +8.3% and +21.5%, respectively
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