Scientists have made the first nickel oxide material that shows clear signs of superconductivity — the ability to transmit electrical current with no loss. Also known as a nickelate, it's the first unconventional superconductor that is very similar to copper oxides, or cuprates, which indicated that superconductors could someday operate at near-room-temperature and revolutionize electronic devices, power transmission, and other technologies. Those similarities may show that nickelates could also superconduct at relatively high temperatures.
At the same time, the new material is different from cuprates in fundamental ways; for example, it may not contain a type of magnetism that all superconducting cuprates have and this could overturn theories of how these unconventional superconductors work.
Ever since the cuprate superconductors were discovered, scientists have worked to make similar oxide materials based on nickel, which is next to copper on the periodic table of the elements. But making nickelates with an atomic structure that's conducive to superconductivity turned out to be unexpectedly challenging.
Research began with a perovskite — a material defined by its unique, double-pyramid atomic structure — that contained neodymium, nickel, and oxygen. The doped the perovskite was doped by adding strontium — a common process that adds chemicals to a material to make more of its electrons flow freely. This stole electrons away from nickel atoms, leaving vacant “holes.” The material then was unstable, making the next step — growing a thin film of it on a surface — challenging.
Once that was done, the film was cut into tiny pieces, loosely wrapped in aluminum foil, and sealed in a test tube with a chemical that neatly removes a layer of its oxygen atoms — much like removing a stick from a wobbly tower of Jenga blocks. This flipped the film into an entirely new atomic structure — a strontium-doped nickelate.
Further testing revealed that the nickelate was superconducting in a temperature range from 9-15 Kelvin with possibilities of higher temperatures ahead. Future work will involve doping the nickelate material in various ways to see how this affects its superconductivity across a range of temperatures and determine whether other nickelates can become superconducting.