Agenda

Résumé : 

Quantum materials possess extraordinary properties, making them highly promising for next-generation electronic devices and quantum information processing. 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. 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. Notably, the unique combination of aberration-corrected scanning transmission electron microscopy (STEM) and in situ reflection high-energy electron diffraction (RHEED) assisted oxide molecular beam epitaxy (MBE) techniques enables us to engineer novel interface properties with precise control at the atomic scale.^[1]
In this talk, I will present our research on MBE-grown complex oxide heterostructures and underline the crucial role of STEM techniques in unraveling the intriguing properties at the interfaces. Using high-angle annular dark-field (HAADF) and annular bright-field (ABF) imaging, electron energy-loss spectroscopy (EELS), and energy-dispersive X-ray spectroscopy (EDXS), we demonstrated that (i) interface superconductivity and interface sharpness can be tuned with epitaxial design^[2–5], (ii) charge transfer and local magnetism can be tailored by strain^[6], (iii) sharper superconducting interfaces can be realized down to one monolayer thickness but with a cost of filamentary superconducting behavior^[7], and (iv) anisotropic magnetism and superconductivity can be tuned via “bi-directional” growth^[8]. Our findings further highlight that the sharpness of the interfaces requires a meticulous definition since structurally perfect and coherent interfaces may exhibit dissimilar chemical sharpness that dominates the physical properties.^[9]

References
[1]        Y. E. Suyolcu^*, G. Christiani, P. A. van Aken, G. Logvenov, J. Supercond. Nov. Magn. 33, 107 (2020).
[2]        Y. E. Suyolcu^*, Y. Wang, W. Sigle, F. Baiutti, G. Cristiani, G. Logvenov, J. Maier, P. A. van Aken, Adv. Mater. Interfaces, 4, 1700737 (2017).
[3]        Y. E. Suyolcu^*, J. Sun, B. H. Goodge, J. Park, J. Schubert, L. F. Kourkoutis, D. G. Schlom, APL Mater. 9, 021117 (2021).
[4]        N. Bonmassar^*, G. Christiani, U. Salzberger, Y. Wang, G. Logvenov, Y. E. Suyolcu^* & P. A. van Aken, ACS Nano 17, 11521 (2023).
[5]        N. Bonmassar^*, G. Christiani, T. Heil, G. Logvenov, Y. E. Suyolcu^* & P. A. van Aken, Adv. Sci. n/a, 2301495 (2023).
[6]        Y.-M. Wu^*, Y. E. Suyolcu^*, G. Kim, G. Christiani, Y. Wang, B. Keimer, G. Logvenov, P. A. van Aken, ACS Nano 15, 16228 (2021).
[7]        Y. E. Suyolcu^*, Y.-M. Wu, G. Kim, G. Logvenov, P. A. van Aken, submitted, (2024).
[8]        N. Bonmassar^*, G. Christiani, M. Brucker, G. Logvenov, Y. E. Suyolcu^* & P. A. van Aken, Adv. Funct. Mater. n/a, 2314698 (2024).
[9] 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. G. Kim, Dr. B. H. Goodge, Dr. J. Sun, N. Bonmassar, and G. Cristiani. The results to be presented are the output of valuable collaborations completed at the Max Planck Institute for Solid State Research, Germany, and at Cornell University, USA.