Synthesis and physical properties of new SUPERconducting NICKEL oxides – SUPERNICKEL

Superconductivity is a fascinating quantum state of condensed matter. Its study and understanding have always aroused immense interest in fundamental physics, but also in materials science and its exploitation leads to numerous technological applications: lossless current transport, energy storage, quantum computation or sensors with unprecedented resolution. In 1986, the discovery of high Tc superconductivity in cuprates allowed the acceleration of enormous progress, both experimentally and theoretically, in several areas of condensed matter physics. However, the origin of high Tc superconductivity is still an unresolved problem; One of the main reasons is the complexity of the physics of cuprates resulting from multiple interactions in competitions (magnetic fluctuations, strong electronic correlations, charge-network coupling, etc.) and nearby orders (charge density wave, antiferromagnetism, pseudo-gap, etc.). The emergence of superconductivity in nickelates, structural and electronic “cousins” of cuprates, was eagerly awaited, but only postponed in 2018 in LaNiO3 / (La, Sr) MnO3 superlattices and in August 2019 in thin layers of the “Infinite phase” Nd0.8Sr0.2NiO2 / SrTiO3, due to the inherently complex chemical processes to stabilize this phase. The SUPERNICKEL project will explore the chemical, structural, physical and electronic properties of new superconducting nickelates, using a transversal approach involving the synthesis of thin films, superlattices and massive materials, the crystallochemistry of the solid, a large battery of macroscopic probes. and experimental microscopic (magneto-transport, X-ray diffraction, photoemission spectroscopy, among others) and theory. Our objectives are to determine the nature and symmetries of the superconducting state, the origin of the interaction forming Cooper pairs, by clarifying the similarities and differences between nickelates and cuprates. Over the past few months, we have focused our efforts on mastering the complex protocol allowing to stabilize the phase of infinite layers and to synthesize the superconducting nickelate.We have already obtained samples with good nominal compositions and close to superconducting instability, and we are confident that very soon, after optimizing their synthesis, we will be one of the few groups in the world to have good quality superconducting nickelates. . In parallel, we will work on other nickelate phases. The possibility of synthesizing and studying in depth, in addition to thin films and superlattices, bulk nickelates will also be a unique approach of SUPERNICKEL. We expect from the thin film / solid material comparison essential and potentially unique information on the specificity of the thin film / substrate form in the emergence of superconductivity. Our multi-approach strategy integrates design, development, detailed crystallochemical characterization, exploration of the physical and electronic properties of normal and superconducting states and theoretical modeling. The SUPERNICKEL consortium thus covers a wide range of know-how in all the essential fields and techniques necessary to tackle this problem: oxide chemistry for the synthesis of massive and thin layers, crystallography, strong correlations, magneto-transport, structure. electronics, magnetism and superconductivity. We also hope that beyond the SUPERNICKEL consortium, the dynamics of this project will become a strong pillar to consolidate and revitalize the French community working in the wider field of new superconductors.