Synthesis, Study and Manipulation of Superconducting Nickelates

The discovery of superconductivity in nickelates in 2019 represented one of the most important steps for decades in the study of unconventional superconductivity.  The initial discovery of high temperature superconductivity in (La,Ba)2CuO4 by Bednorz and Muller in 1986 launched extensive study into the family of superconducting cuprates which has since expanded to include a variety of chemical formulas and crystal structures, all of which are united by superconducting atomic planes of square-planar CuO2 and nominal 3d9 electron filling of the copper ions. It was theoretically predicted more than 20 years ago that compounds containing nickel -- neighboring copper on the periodic table -- with similar structural and electronic configuration may also host superconductivity. Synthesis of these proposed superconducting nickelates, however, turned out to be very difficult, explaining why it took so long to be achieved [1].

            Now that superconductivity has been stabilized in thin film hole-doped infinite-layer rare-earth nickelates, RNiO2 (R = La, Nd, Pr), the quest is on to understand this close isoelectronic analogue to the high-Tc cuprates. Already experiments have revealed a number of distinctions between the nickelate and cuprate superconductors, including differences in the hybridization, charge-transfer energy, and pairing mechanism [2-4]. At the same time, calculations have suggested that depletion of the rare-earth bands could result in a Fermi surface reconstruction that renders the nickelates cuprate-like despite these differences.

            This highly collaborative international project will seek to explore this issue and other physical properties of superconducting nickelates.   We also plan to synthesize the materials by alternative methods, in collaboration with groups at the Max Planck Institute for Solid State Physics (Stuttgart) and Stanford University (USA). Investigation of the nickelate response to external stimuli, such as uniaxial and biaxial strain, will be carried out at MPI-CPfS in Dresden and in labs across Europe, the UK, and United States. Angle-resolved photoemission spectroscopy (ARPES) measurements will be carried out at international synchrotron facilities with photoemission beam lines. Additional sample characterization by high-resolution scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) may be performed at Cornell University (USA). The successful student will therefore gain experience with state-of-the-art condensed matter physics and materials science techniques.  We seek a careful and thorough experimentalist with data processing and practical engineering skills.

[1] D. Li, K. Lee, B. Y. Wang, M. Osada, S. Crossley, H. R. Lee, Y. Cui, Y. Hikita, & H. Y. Hwang
Superconductivity in an infinite-layer nickelate
Nature, 572(7771), 624-627 (2019)
[2] M. Hepting, D. Li, C. J. Jia, H. Lu, E. Paris, Y. Tseng, X. Feng, M. Osada, E. Been, Y. Hikita, Y.-D. Chuang, Z. Hussain, K. J. Zhou, A. Nag, M. Garcia-Fernandez, M. Rossi, H. Y. Huang, D. J. Huang, Z. X. Shen, T. Schmitt, H. Y. Hwang, B. Moritz, J. Zaanen, T. P. Devereaux, & W. S. Lee
Electronic structure of the parent compound of superconducting infinite-layer nickelates
Nature Materials, 19(4), 381-385 (2020)
[3] B. H. Goodge, D. Li, K. Lee, M. Osada, B. Y. Wang, G. A. Sawatzky, H. Y. Hwang, & L. F. Kourkoutis
Doping evolution of the Mott–Hubbard landscape in infinite-layer nickelates
Proceedings of the National Academy of Sciences, 118(2), e2007683118. (2021).
[4] H. Lu, M. Rossi, A. Nag, M. Osada, D. F. Li, K. Lee, B. Y. Wang, M. Garcia-Fernandez, S. Agrestini, Z. X. Shen, E. M. Been, B. Moritz, T. P. Devereaux, J. Zaanen, H. Y. Hwang, K.-J. Zhao, & W. S. Lee
Magnetic excitations in infinite-layer nickelates
Science, 373(6551), 213-216 (2021)
[5] K. Lee, B. Y. Wang, M. Osada, B. H. Goodge, T. C. Wang, Y. Lee, S. Harvey, W. J. Kim, Y. Yu, C.  Murthy, S. Raghu, L. F. Kourkoutis, H. Y. & Hwang
Character of the "normal state" of the nickelate superconductors
arXiv:2203.02580 (2022)

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