Y. Eren Suyolcu

Dopant size effects on novel functionalities: High-temperature interfacial superconductivity

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.

Correcting the linear and nonlinear distortions for atomically resolved STEM spectrum and diffraction imaging

We report a software tool for post-correcting the linear and nonlinear image distortions of atomically resolved 3D spectrum imaging as well as 4D diffraction imaging. This tool improves the interpretability of distorted scanning transmission electron microscopy spectrum/diffraction imaging data.

Linking Dopant Distribution and Interatomic Distortions at La 1.6 Mo.4CuO 4 /La2CuO4 Superconducting Interfaces

The crystal structures of complex oxide materials are highly adaptable to changes in composition and this compatibility provides the opportunity of synthesizing them in different forms, such as ultrathin films and/or heterostructures. Oxide heterostructures exhibit remarkable electronic properties which do not exist in bulk forms and the emergent phenomena occurring at the interfaces are impressive [1]. One of the exciting interface effect is high temperature interfacial superconductivity discovered in heterostructures consisting of an insulating La2CuO4 (LCO) and metallic La1.55Sr0.45CuO4 (LSCO) layers, while neither of these layers is superconducting [2].

High-Temperature Thermoelectricity in LaNiO3–La2CuO4 Heterostructures

Transition metal oxides exhibit a high potential for application in the field of electronic devices, energy storage, and energy conversion. The ability of building these types of materials by atomic layer-by-layer techniques provides a possibility to design novel systems with favored functionalities. In this study, by means of the atomic layer-by-layer oxide molecular beam epitaxy technique, we designed oxide heterostructures consisting of tetragonal K2NiF4-type insulating La2CuO4 (LCO) and perovskite-type conductive metallic LaNiO3 (LNO) layers with different thicknesses to assess the heterostructure-thermoelectric property-relationship at high temperatures. We observed that the transport properties depend on the constituent layer thickness, interface intermixing, and oxygen-exchange dynamics in the LCO layers, which occurs at high temperatures. As the thickness of the individual layers was reduced, the electrical conductivity decreased and the sign of the Seebeck coefficient changed, revealing the contribution of the individual layers where possible interfacial contributions cannot be ruled out. High-resolution scanning transmission electron microscopy investigations showed that a substitutional solid solution of La2(CuNi)O4 was formed when the thickness of the constituent layers was decreased.

Oxygen Octahedral Picker: A Digital Micrograph Script Tool for Extracting Quantitative Information From HAADF and ABF Images

The multifaceted magnetic, electrical, and structural functionalities of perovskite oxides are underpinned by the distortions of the crystal lattice [1]. These distortions include the displacement of cations, deformation of oxygen octahedra (BO6, where B is a transition metal atom), and collective tilts of the octahedral network. Controlling and engineering these distortions in the constituent oxides are crucial in designing and fabricating hetero-structures with novel functional properties that are absent in the bulk form. Atomistic understanding of these distortions and elucidation of their influence on the final properties requires imaging and measuring of atomic positions of both cations and oxygen. With the application of spherical aberration (Cs) correctors, sub-Angstrom atomic resolution is nowadays regularly achievable in both TEM and STEM. The recent application of the annular bright-field (ABF) imaging technique in perovskite oxides has become increasingly popular, as it enables simultaneous imaging of heavy and light elements and allows for simultaneous acquisition of other signals [2, 3]. Quantitative analysis of atom-column positions in high-resolution STEM images helps us gain new insight into materials behavior and address material problems. However, there are rare resources about methods for indexing atomic column positions in atomic resolution images, especially for the case of ABF images, as well as for the measurement accuracy.