Pure nickel oxide research refutes hydrogen-superconductivity link

Physicists from the National University of Singapore (NUS) have synthesized very pure superconducting materials and redefined the critical role of hydrogen in the newly discovered nickel-oxide superconductors.

Their findings were published concurrently in the journals Nature Communications and Physical Review Letters.

Superconductivity is an exciting phenomenon where electrical resistance disappears, and it holds transformative potential for revolutionizing energy technologies. Despite its potential, the origin and fundamental mechanism of superconductivity remain one of the greatest mysteries in physics.

More than a century after the discovery of superconductivity, only a subgroup of superconducting materials, mainly elemental metals and hydrogen-based compounds, can be explained using the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity, which was awarded the Nobel Prize in Physics in 1972.

However, there exists a large group of superconducting materials classified as “unconventional superconductors” in which their superconducting mechanism cannot be explained by this theory. The recently discovered nickel oxide superconductor is one such example.

In a recent study published in the journal Nature, researchers proposed that hydrogen plays a key role in nickel oxide superconductivity. Using an ionic detection technique known as secondary ion mass spectrometry which measures the concentration of hydrogen, the researchers suggested a link between hydrogen and superconductivity, attributing the phenomenon to mechanisms consistent with the BCS theory.

A research team led by Professor Ariando from the Department of Physics at NUS in two independent efforts with various international collaborators (Agency of Science and Technology and Research (A*STAR) in Singapore, National Institute of Standards and Technology (NIST), Harvard University, University of Southern California, Arizona State University, and Cornell University from the United States of America) synthesized very pure superconducting nickel oxide samples to reexamine the role of hydrogen in nickel oxide superconductors.

Contrary to the previous findings reported in Nature, Prof Ariando’s team and collaborators conclusively demonstrated that there is an insignificant presence of hydrogen in the pure nickel oxide materials. They also established that there is no correlation between hydrogen and superconductivity.

One of the authors, Mr. Lin Er Chow, a Ph.D. student said, “Surprisingly, hydrogen is not even abundantly present in pure superconducting nickel oxide. This observation suggests that hydrogen does not play an important role in the origin of superconductivity in these materials.”

“These findings help guide the research direction towards understanding the fundamental superconducting mechanism of the high critical-temperature unconventional superconductors,” added Prof Ariando.