Advanced Epitaxy for Complex Oxide Interfaces

Quantum materials possess extraordinary properties, making them highly promising for next-generation electronic devices and quantum information processing. Among these materials, transition-metal oxide heterostructures provide a versatile playground for quantum phenomena, including high-temperature superconductivity, magnetism, and metal-to-insulator transition. The origin of these phenomena is the competition between different degrees of freedom, such as charge, orbital, and spin, which are interrelated with the crystal structure, the oxygen stoichiometry, and the doping dependence. Therefore, understanding the intricate structure-property relationship in these materials is crucial for harnessing their full potential.
The unique combination of oxide molecular-beam epitaxy (MBE) and aberration-corrected scanning transmission electron microscopy (STEM) techniques allows the engineering of novel interface properties with precise control at the atomic scale. Combining different oxide layers through heterostructural design opens access to interface physics and leads to engineering interface properties, where the degrees of freedom can be artificially modified.
In this talk, I will present our research and different approaches to designing complex oxide interfaces that underlines the remarkable potential of oxide-based quantum materials and the crucial role of STEM techniques in elucidating their novel properties. Through different epitaxial designs and approaches, we demonstrate that (i) through specific flux calibration and precise control of growth conditions, the sharpest interfaces at a-axis YBa₂Cu₃O_7−x multilayers can be achieved, (ii) superconductivity can be tuned via epitaxial integration of ultra-thin slabs, (iii) sharper superconducting interfaces can be realized down to one monolayer thickness but with a cost of filamentary superconducting behavior, and (iv) anisotropic magnetism and superconductivity can be tuned via bi-directional growth. ^[1-6]

References
[1] Y. E. Suyolcu^*, J. Sun, B. H. Goodge, J. Park, J. Schubert, L. F. Kourkoutis, D. G. Schlom, APL Materials 2021, 9, 021117.
[2] Y.-M. Wu, Y. E. Suyolcu^*, G. Kim, G. Christiani, Y. Wang, B. Keimer, G. Logvenov, P. A. van Aken, ACS Nano 2021, 15, 16228.
[3] N. Bonmassar, G. Christiani, U. Salzberger, Y. Wang, G. Logvenov, Y. E. Suyolcu^* and P. A. van Aken, ACS Nano 2023, 17, 11521.
[4] Y. E. Suyolcu^* et al., unpublished.
[5] N. Bonmassar, G. Christiani, M. Bruckner, G. Logvenov, Y. E. Suyolcu^* and P. A. van Aken, Adv. Func. Mat., 2024, 34, 2314698.
[6] I acknowledge all valuable scientists for their significant contributions to the work presented, especially Prof. P. A. van Aken, Prof. D. G. Schlom, Prof. B. Keimer, Prof. L. F. Kourkoutis, Dr. G. Logvenov, Dr. Y.-M. Wu, Dr. N. Bonmassar, Dr. G. Kim, Dr. B. H. Goodge, and Dr. J. Sun.