New leap in understanding nickel oxide superconductors

In the 35 years since the first unconventional “high-temperature” superconductors were discovered, researchers have been racing to find one that could carry electricity with no loss at close to room temperature. This would be a revolutionary development, allowing things like perfectly efficient power lines, maglev trains and a host of other futuristic, energy-saving technologies.

But while a vigorous global research effort has pinned down many aspects of their nature and behavior, people still don’t know exactly how these materials become superconducting.

So the discovery of nickelate’s superconducting powers by SIMES investigators three years ago was exciting because it gave scientists a fresh perspective on the problem.

Since then, SIMES researchers have explored the nickelates’ electronic structure – basically the way their electrons behave – and magnetic behavior. These studies turned up important similarities and subtle differences between nickelates and the copper oxides or cuprates – the first high-temperature superconductors ever discovered and still the world record holders for high-temperature operation at everyday pressures.

Since nickel and copper sit right next to each other on the periodic table of the elements, scientists were not surprised to see a kinship there, and in fact had suspected that nickelates might make good superconductors. But it turned out to be extraordinarily difficult to construct materials with just the right characteristics.

“This is still very new,” Lee said. “People are still struggling to synthesize thin films of these materials and understand how different conditions can affect the underlying microscopic mechanisms related to superconductivity.”

Frozen electron ripples

CDWs are just one of the weird states of matter that jostle for prominence in superconducting materials. You can think of them as a pattern of frozen electron ripples superimposed on the material’s atomic structure, with a higher density of electrons in the peaks of the ripples and a lower density of electrons in the troughs.

As researchers adjust the material’s temperature and level of doping, various states emerge and fade away. When conditions are just right, the material’s electrons lose their individual identities and form an electron soup, and quantum states such as superconductivity and CDWs can emerge.

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