Functionality and Interface Design in Complex Oxides
The "Functionality and Interface Design in Complex Oxides" group is dedicated to the atomic-scale design and realization of oxide-based quantum materials. Our focus is on bridging epitaxial growth with atomic-layer precision and extensive atomic-resolution scanning transmission electron microscopy (STEM) techniques to tailor two-dimensional phenomena at transition metal oxide heterostructure interfaces. Our research spans several complex oxides, including thin films, heterostructures, and single crystals. We grow epitaxial films in the Thin Film Technology Group and the Department Mannhart using ozone-assisted molecular beam epitaxy (MBE), pulsed laser deposition (PLD), and thermal laser epitaxy (TLE), respectively, and collaborate with the Department Keimer for single crystal research. Materials of interest include (but are not limited to) cuprates, nickelates, manganates, cobaltates, ruthenates, and rhodates, either in epitaxial thin film form or as single crystals. We probe the local structural and electronic properties using comprehensive STEM techniques such as high-angle annular dark-field (HAADF) and annular bright-field (ABF) imaging, electron energy-loss spectroscopy (EELS), energy-dispersive X-ray spectroscopy (EDXS) and 4D-STEM. Our combined approach at the atomic scale paves the way for revealing new functionalities and applications in quantum materials.
Epitaxial growth of complex oxides enables the fabrication of materials layer by layer in fashion design, allowing for intervention during film growth and facilitating the creation of artificial materials and unique interfaces. Epitaxial layers are influenced by the boundary conditions, leading to changes in their properties due to strain, polar discontinuities, and octahedral connectivity (mis)matching.
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Complex oxide heterostructures provide a versatile playground for quantum phenomena with extraordinary properties, making them highly promising for next-generation electronic devices and quantum information processing. The origin of these phenomena is the competition between different degrees of freedom, such as charge, orbital, and spin, which are related to the crystal structure, the oxygen stoichiometry, and the doping dependence.
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The “nickelate family” has been the subject of interest in many studies due to its rich phase diagram, including metal-insulator transitions (MIT), magnetism, and superconductivity in topotactically reduced infinite-layer (IL) compounds and high-temperature superconductivity in Ruddlesden-Popper (RP) phases. Their pronounced structure-property relationship and high tolerance to structural and compositional changes allow tuning of the strength of electronic and magnetic correlations.
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Ultrathin QMs offer exclusive access to their emergent properties because they are sensitive to material surfaces and interfaces. Due to the strong confinement of electrons in reduced dimensions, they can be easily manipulated by strain, epitaxial design, electric fields, and control of charge carrier density.
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