Research News

In 2019, a new superconductor was discovered amongst the nickelates (nickel-based oxides), but only now have the underlying physical and chemical similarities with their Periodic-Table twin superconductors, the cuprates, been identified.

Researchers have identified the underlying physical and chemical properties of a recently discovered superconductor in nickelate. The theoretical model for describing this new superconductor was achieved, and now launched to explore the high-temperature superconductors in the nickelates. For the first time, researchers were able to explain the electronic structure precisely and set up a parameterized theoretical model for the superconductivity in nickelates.

The findings were published in the Physical Review X on 13 October.

The first superconductor was discovered in 1911 by a Dutch physicist when he cooled the mercury down to within a few degrees of absolute zero, and found that it lost all resistance to the flow of electrical current. Since then, the hunt has been on for other materials that exhibit this phenomenon but remain superconducting at higher temperatures, so-called “high-temperature superconductors”.

For some time, cuprates (copper-based oxides) have been investigated as a promising high-temperature superconductor candidate, although the reported critical temperature remains below room temperature. In 2019, researchers discovered a new superconductor in nickelate (nickel-based oxide).

“It is of special importance to understand the differences and similarities at the label of the constituent electrons and their motion inside materials,” said Atsushi Hariki, Assistant Professor at Osaka Prefecture University. “Identifying how these twin superconductors differ at a much more fine-grained level of detail may offer us a will guide to elevating the critical temperature even as the nickelate remains superconducting.”

To investigate the relations between these twin superconductors, the researchers first needed to determine a series of parameters that enter in the theoretical model that describes superconductors. The parameter of particular interest was the “charge transfer energy”, which describes the energy necessary for an electron to move from a nickel atom to an oxygen atom. Once this had been identified, they were able to draw the orbital of the traveling electrons inside the superconductors and to examine the differences between the cuprate and nickelate superconductors.

The charge transfer energy is buried deep in the energy spectrum, which has many contributing factors, e.g., chemical bonding, Coulomb interaction between nickel electrons, electron concentration, and so on. To derive its value from experimental core-level x-ray spectroscopy data, the researchers developed a computational method (based on local density approximation combined with dynamical mean-field theory).

With the aid of a high-performance supercomputer, this method allowed them to examine the charge transfer energy as well as other model parameters of the new nickelate superconductors via a face-to-face comparison with the x-ray spectroscopy data (using core-level x-ray spectroscopy and resonant inelastic x-ray scattering techniques).

The hope now is to use this information to improve the material still further, for producing new nickelates whose superconductivity persists up to even significantly higher temperatures, and to explore the underlying mechanism of the superconducting phenomena in the nickelates.

Other contributors include first author Keisuke Higashi, Graduate School of Engineering at Osaka Prefecture University; Mathias Winder and Jan Kuneš, Institute of Solid State Physics at Technischen Universität Wien.

We simulated resonant inelastic x-ray scattering (RIXS) spectra of infinite-layer nickelate. A comparison with the experimental data allowed us to derive the key parameters (charge transfer energy) determining the motion of electrons in the material. The crystal structure of the nickelate is shown.

Paper Information

Journal title: Physical Review X
Paper title: Core-level x-ray spectroscopy of infinite-layer nickelate: LDA+DMFT study
DOI: 10.1103/PhysRevX.11.041009
URL: Physical Review X (ACS Publications Website)

Funding Information

Japan Society for the Promotion of Science (JSPS) KAKENHI : Grant No. 21K13884
The European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program : Grant Agreement No. 646807-EXMAG

Original Article

URL: http://www.osakafu-u.ac.jp/english-news/pr20211014e

Media Contact

Department of Electronics Mathematics and Physics, Graduate School of Engineering
Dr. Atsushi HARIKI
E-mail hariki[at]pe.osakafu-u.ac.jp
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