Long-lost sister of high-temperature copper-oxide superconductor discovered

NUS physicists have realised superconductivity in lanthanide nickel-oxide, answering a theoretical prediction made about three decades ago. This enables a new way to achieve and understand high-temperature superconductivity.

Superconductivity occurs when the temperature of a superconductive material goes below a certain value, known as the critical temperature, their electrical resistance drops to zero. This means that it becomes possible to transmit a large amount of electricity with zero energy losses. Such a phenomenon will have profound influence on the development of future technological applications. Since its discovery more than a century ago, the bottleneck of this vision has been the low critical temperature at which superconductivity occurs. This is around the boiling point of liquid helium (around -269℃, far colder than the temperature at which most modern electronics operate). To develop superconducting materials of higher critical temperature or even at room temperature, one needs to study the mechanism of "high-temperature" superconductivity found in compounds consisting of copper and oxygen atoms as its building blocks. These are known as cuprate compounds and lanthanide copper-oxide (La-Ba-Cu-O) is the first copper-oxide superconductor discovered in this family. The copper-oxygen building block has been envisioned by many researchers as a critical ingredient to achieve superconductivity at higher temperatures. Although various theories associated with the presence of superconductivity in cuprate compounds have been proposed, there has been no consensus on the actual mechanism.

One ideal route for exploring the mechanism of the high temperature superconductors is to search for other material systems that closely resemble cuprate compounds but do not contain copper in their building blocks. It was envisioned in the early 1990s that the closest "twin sister" of copper-oxide is nickel-oxide. Nickel is the element which is located next to copper in the periodic table and it has similar material properties. However, three decades of experimental efforts have failed to realise superconductivity in the lanthanide nickel-oxide, diminishing hope to search for and understand higher temperature superconductivity.

In 2021, Associate Professor Ariando's group in the Department of Physics, National University of Singapore successfully synthesised a lanthanide nickel-oxide superconductor. They achieved this by performing unique material synthesis and control with atomic precision. Nickel and oxygen atoms were first carefully sandwiched between lanthanum and calcium atoms. Next, the oxygen atoms were removed in an alternating fashion from the stack containing a complex arrangement of these four atoms. This is similar to the Jenga game with the building blocks representing an individual atom in a lanthanide calcium nickel-oxide compound (La_1-xCa_xNiO₂). The group eventually demonstrated superconductivity behaviour in La_1-xCa_xNiO₂, ending the decades-long quest.

Apart from exhibiting zero electrical resistance, superconductors also exhibit perfect diamagnetism (Meissner effect). This effect can fully expel external magnetic fields and is the science behind the "magnetic-levitation train" for low-energy high-speed transportation. The existence of superconductivity in a new material can only be proven when both effects are observed. Prof Ariando and his collaborators successfully improved the material quality and demonstrated perfect diamagnetism in nickel-oxide superconductors. The research team has since performed further studies on this new found nickel-oxide superconductor.

Prof Ariando said, "Our breakthrough has become the embryo to the birth of a new superconducting era "the nickel age", providing a new solid playground for experimentalists and theorists alike in this decades-long endeavour for high temperature superconductivity."

More information:
S. W. Zeng et al, Observation of perfect diamagnetism and interfacial effect on the electronic structures in infinite layer Nd0.8Sr0.2NiO2 superconductors, Nature Communications (2022). DOI: 10.1038/s41467-022-28390-w

Superconductivity in infinite-layer nickelate (La,Ca)NiO2, Science Advances (2022). DOI: 10.1126/sciadv.abl9927

Provided by National University of Singapore