Developing new techniques to design and discover novel quantum materials and architectures poses an exciting frontier in condensed-matter research. In particular, synthesis of additional superconductors, especially those with unusual symmetries of superconducting order parameters and/or exotic pairing mechanisms, opens new doors to future applications in quantum devices. In this seminar, I will present research efforts on atomic-scale growth and engineering of such unconventional superconductors in complex oxide heterostructures, based on two extraordinary examples: SrTiO3 and nickelates. In the first part, I will elucidate the “polar catastrophe” scenario as the origin of the two-dimensional electron system at the celebrated LaAlO3/SrTiO3 interfaces and discuss low-dimensional superconductivity in the related heterostructures. I will also review the on-going investigations on the nature of SrTiO3 superconductivity and their implications. In the second part, I will present the recent observation of superconductivity in an infinite-layer nickelate compound [D. Li et al., Nature 572, 624 (2019)] and the study of its superconducting phase diagram. This system is of particular interest due to its potential relationship with the high-Tc cuprate superconductors, in that they share a similar crystal structure and starting electronic configuration. I will also highlight the key aspects of its electronic and magnetic structures, which are inherently distinct from cuprates. Finally, I will suggest how new applications of kinetic-based synthetic approaches in oxide heterostructures provide a broad opportunity to create novel quantum systems in previously inaccessible ways.
Dr Danfeng Li is currently a Postdoctoral Research Fellow at Stanford University. Danfeng obtained his BEng from Zhejiang University and MPhil from The Hong Kong Polytechnic University. Shortly after earning his PhD in the Department of Quantum Matter Physics at University of Geneva (2016; thesis advisor: Prof. Jean-Marc Triscone), Danfeng joined Stanford University as a Swiss National Science Foundation postdoctoral fellow (2017), working with Prof. Harold Hwang. His main research interests span across condensed-matter physics and materials science, with focus on atomic-scale fabrication of oxide heterostructures and nanomembranes, kinetic based synthesis of unconventional quantum materials, low-dimensional superconductivity, oxide interfaces for emergent states. Recently, a team led by Dr. Li and Prof. Hwang discovered the first nickelate superconductor.
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