Modified Nickel Materials May Improve Understanding of High Temperature Superconductivity

Figure 1: Electrons (lilac) interact strongly with each other when they move through a layer of NiO2 nickel material, which can serve as a model for high-temperature superconductivity (nickel = gray, oxygen = red). (Image courtesy of Marie Ishida from the RIKEN Center for Emerging Materials Science.) Courtesy: RIKEN for the Center for Emerging Materials Science.

The hunt for high-temperature superconductors can be helped by the calculations of physicists RIKEN, who revealed the behavior of electrons in a material made of nickel oxide.

Superconductors can carry electricity without resistance, and are used to create powerful electromagnets or sensitive instruments for measuring magnetic fields.

common superconductivity depends on the form of electron pairing, which occurs only at extremely low temperatures, so superconducting devices must be cooled by expensive liquefied gases. But about 30 years ago, researchers found that some cuprate materials can become superconductors at relatively high temperatures, up to -140 degrees Celsius. The main reason for this high-temperature superconductivity is still not understood.

In 2019, researchers found that strontium-doped nickel-neodymium oxide (Nd0.8Sr0.2Nio2) there may be superconductivity below -258 degrees Celsius. This discovery did not attract attention because of the temperature, but because this nickelate material has a very similar crystalline structure with cuprates and can serve as a test bench to better understand how superconductivity in these materials works.

Nickel-plated material consists of alternating layers of Nd and NiO2Yusuke Nomura of the RIKEN Center for Emergent Matter Science and colleagues have now studied how interactions between specific electrons in these two layers can affect superconductivity.

Team calculations showed that electrons in NiO2layer interact strongly with each other, which is similar to cuprates, where there is a strong correlation in CuO2 The layer is believed to play a key role in their high temperature superconductivity. However, there is a difference between nickelates and cuprates: in nickelates, the electrons in the neodymium layer are partially occupied and form a Fermi pocket, a relatively small region in the Brillouin zone surrounded by the Fermi surface. These pockets do not appear in cuprates, which can make nickel material an imperfect analogue of cuprates.

The Nomura team used computational models to explore the possibility of removing pockets by changing the chemical composition of the material and therefore creating nickelate It is better for cuprates. They found that two compounds could meet the requirements: sodium, neodymium, nickel oxide (NaNd2Nio4) and sodium-calcium-nickel oxide (NaCa2Nio3) “If the proposed nickelates are synthesized, they will become real nickel analogues of cuprate superconductors,” notes Nomura.

“The next step is a more systematic clarification of the differences and similarities between nickelates and cuprates and a deeper understanding of the superconducting mechanism in both systems,” he adds.

The first detailed electronic study of a new nickel superconductor

Additional Information:
Yusuke Nomura et al. Formation of a two-dimensional one-component correlated electronic system and band engineering in a NdNiO nickel superconductor2, Physical Review B (2019). DOI: 10.1103 / PhysRevB.100.205138

Modified Nickel Materials May Improve Understanding of High Temperature Superconductivity (2020, March 13)
retrieved March 13, 2020

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