Abstract
The 2019 discovery of high temperature superconductivity in layered nickelate films, Nd1-xSrNiO2, has galvanized a community that has been studying nickelates for more than 30 years both as cuprate analogs and in their own right. On the surface, infinite layer nickelates, and their multilayer analogs, should be promising candidates based on our understanding of cuprates: square planar coordination and a parent d9 configuration that places a single hole in a dx2-y2 planar orbital makes nickelates seem poised for superconductivity. But creating crystals and films of sufficient quality of this d9 configuration in Ni1+ has proven to be a synthetic challenge, only recently overcome. These crystalline specimens are opening windows that shed new light on the cuprate-nickelate analogy and reveal nuances that leave the relationship between cuprates and nickelates very much an area open to debate. This Perspective gives a qualitative, phenomenological account of these newly discovered superconductors and multilayer members of the infinite layer nickelate family. The focus is on our current understanding of electronic and magnetic properties of these materials as well as some future opportunities, explored from the viewpoint of synthetic challenges and some suggested developments in materials discovery and growth to make further progress in this rejuvenated field.
Highlights
Like the soil, mind is fertilized while it lies fallow, until a new burst of bloom ensues [1]
With superconductivity discovered in epitaxial thin films of the “infinite-layer” d9 nickelate (Nd,Sr)NiO2 by Harold Hwang [2] and his Stanford collaborators in mid-2019 and more recently by Julia Mundy [3] of Harvard in the five-layer nickelate Nd6Ni5O12, a decades-long dream has been realized
Their discoveries and other exciting new findings in d9 layered nickelate materials rest on breakthroughs in thin film and single crystal growth that have allowed old ideas to take on a new life, and renewed enthusiasm to explore the nickelates as a platform to understand high-Tc superconductivity beyond cuprates, a “new burst of bloom.”
Summary
Materials Science Division, Argonne National Laboratory, Lemont, IL, United States. Edited by: Matthias Hepting, Max Planck Institute for Solid State Research, Germany. Creating crystals and films of sufficient quality of this d9 configuration in Ni1+ has proven to be a synthetic challenge, only recently overcome. These crystalline specimens are opening windows that shed new light on the cuprate-nickelate analogy and reveal nuances that leave the relationship between cuprates and nickelates very much an area open to debate. This Perspective gives a qualitative, phenomenological account of these newly discovered superconductors and multilayer members of the infinite layer nickelate family.
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