The scientists used chemical methods to remove a layer of oxygen atoms, converting the material into nickelate. This substance exhibits superconducting properties.
The scientists first doped the perovskite with strontium, and then used chemicals to “remove” the oxygen atomic layer, flipping its atomic structure to form a superconducting nickelate material.
Phys.org website reported on August 28 that scientists from the U.S. Department of Energy’s SLAC National Accelerator Laboratory and Stanford University created the first nickel oxide material with obvious superconducting properties. The material is a potential unconventional superconductor, similar to cuprate superconductors. Since cuprate superconductors were discovered in 1986, scientists have hoped to use them to revolutionize electronic devices and power transmission technology. The similarities between nickelates and cuprates have lit up a new “thinking fire” for scientists: Can nickelates also achieve high-temperature superconductivity? But there are also significant differences between nickelates and cuprates. For example, nickelates have very different magnetic properties than cuprates. This could overturn leading theories about how unconventional superconductors work. Danfeng Li, a postdoctoral researcher at the Stanford Institute for Materials and Energy Sciences, led relevant research and published the research results in the journal Nature. George Sawatzky, professor of physics and chemistry at the University of British Columbia, wrote a review article for Li et al.’s paper: “This is a very important discovery. We need to rethink the electronic structure and superconducting mechanism of these superconducting materials. The academic community will invest a lot Manpower and energy will be devoted to the research of this type of new materials, and various experimental and theoretical work will be gradually improved.”
Ever since scientists discovered copper-based superconductors, they have hoped to create similar oxide materials using copper’s neighbor on the periodic table, nickel. However, making nickel-based superconductors is surprisingly difficult. “As far as we know, nickelates are unstable at high temperatures (about 600 degrees Celsius),” Li said. “So we need to find a material that can grow stably at high temperatures and then transform into the desired structure at low temperatures.”
Li et al. chose to start from a perovskite material with a unique double pyramid atomic structure and dope it with strontium to enhance its electron free mobility. The doping process takes electrons away from the nickel atoms, leaving holes, which the nickel atoms are “a little bit unhappy about” – the material becomes unstable, making the next step of surface film formation extremely challenging. It took Li et al. about half a year to complete this work.
After the film forms, Li cuts it into small pieces, then wraps it in aluminum foil and seals it with some kind of chemical. Chemicals stripped the film of oxygen atoms, leaving it with a completely new atomic structure: strontium-doped nickelate. Further tests showed that the superconducting temperature of nickelate is 9 to 15 Kelvin. Although the temperature is still very low, the possibility of high-temperature superconducting is already available.
Harold Hwang, a professor at SLAC and Stanford University, believes that the research on nickelate materials is still in its infancy, and there is still a lot of work that needs to be improved. He said the scientists hope to change the way the nickelate is doped to understand how the new material’s superconductivity is affected at different temperatures, thereby identifying other nickel-based superconducting materials. In addition, the relationship between the special magnetic structure of new materials and superconductivity is also one of the focuses of researchers.
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