Synthesis and Spectroscopy of Thin Film Nickelate Superconductors

Cornell University, Ithaca NY

Investigators

Abstract

Nontechnical Abstract: The electronic properties of materials are critical to modern civilization and society, enabling technologies such as telecommunications, computing, and information storage and processing. Among these properties, superconductivity is particularly promising for applications in quantum information processing and communication, medical imaging, energy storage and transport, and electronics. The possibility to discover and engineer new superconductors with superior properties, such as higher operating temperatures or larger current densities, is one of the frontiers of modern physics. The objective of this project is to provide a more coherent and global understanding of the long-standing puzzle of high-temperature superconductivity through the investigation of a newly discovered but still enigmatic family of superconductors based on nickel oxides and comparing these materials to the closely related and more well-established family of copper oxide high-temperature superconductors. By achieving a better understanding of these nickel oxide superconductors and comparing their properties with their copper oxide cousins, this project could unlock the key ingredients for discovering higher temperature superconductors. Finally, this project provides crucial training to young scientists in materials synthesis and characterization, outreach activities, and the samples fabricated in these studies supports several scientific collaborations across the country. Technical Abstract: Layered nickelates with a Ni 1+ valence have long been proposed as close electronic analogues to the cuprates and another potential family of high temperature superconductors. The recent discovery of superconductivity at 15 K in doped rare earth nickelates in the infinite layer structure has ignited intense interest in these materials, but there are many open questions about these compounds, including the nature of the superconductivity, their underlying electronic structure, and which aspects are similar or different from the cuprates. The objectives of this project are to synthesize and investigate thin films of infinite layer nickelates using a combination of oxide molecular beam epitaxy and angle-resolved photoemission spectroscopy to address fundamental questions about the nickelates, including the momentum-dependence of the superconducting gap, the presence and nature of a pseudogap, the electronic structure of the parent compounds, and the normal state electronic structure. The research proposed here consists of two primary stages, specifically the synthesis of infinite-layer nickelate thin films, beginning with oxide MBE synthesis of precursor perovskite nickelates, followed by reduction to achieve the infinite layer structure. Next, angle-resolved photoemission spectroscopy addresses crucial questions about these nickelate superconductors, including the nature of the superconducting order parameter, the electronic structure of the parent compound, the evolution of the electronic structure with hole doping into the superconducting state, and the possible existence of a pseudogap. The samples synthesized through this project support a wide number of external collaborations, including optical spectroscopy and magnetic imaging. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.