Superconductor functioning at room temperature - second set

Scientists who published an article in Nature in 2020 describing a superconductor that works at room temperature claim that they conducted additional experiments and used additional data from the original experiment and are now resubmitting it

[Translation by Dr. Moshe Nachmani]

Computer companies will be able, in the near future, to create superconducting quantum computer chips that function at room temperature, thanks to an innovative material developed by researchers from the University of Rochester.

The new material is a superconductor that functions at a temperature of 21 degrees Celsius and at an atmospheric pressure of less than one percent of the normal pressure used in existing superconductors that function at high temperatures. The researchers were mostly surprised by the low atmospheric pressure required.

The researchers from the University of Rochester, together with researchers from the University of Nevada, explain that the electrical resistance inside their innovative material, which consists of lutetium hydride condensed with nitrogen, reaches zero at room temperature. The production of materials with zero electrical resistance at room temperature constitutes the "holy grail" in the field of chemistry and will one day be able to contribute to the fight against climate change by reducing the five percent loss of electricity production in the form of heat during the transmission of electricity in the national grid. At the same time, the researchers have not yet been able to completely verify the structure of the innovative material. In light of the fact that hydrogen atoms are so tiny, it is not easy to characterize them with the help of X-ray diffraction in order to obtain the exact composition and structure of the material.

Several research teams are currently focusing on the development of superconductors at room temperature in hydrogen-rich materials at very high atmospheric pressures between two diamond tips. Such a system is known by the scientific name "diamond anvil cell" (DAC) and it provides very high pressures simply by screwing a number of screws. In the decade that began in 2010, experiments with these high pressures made it possible for various materials, including hydrogen sulfide and lanthanum hydride to become superconductors close to room temperature. At the same time, the lead researcher explains that the size of the largest samples provided to be located between the prongs of the diamonds is approximately 250 microns in diameter, a size that is far from that which would allow the production of superconducting-based electrical cables. Ten degrees C. Doping of carbon atoms helped strengthen and anneal the material, which prevented it from breaking down at higher temperatures and helped every two electrons to pair up, a key requirement for superconductivity to exist. However, this property is only obtained at atmospheric pressure 2020 million times that of Earth. This finding was examined in detail in light of irregularities revealed in the superconductivity procedure by the researchers and was ultimately found to be incorrect. The scientists are resubmitting the data after processing previously untested raw data.

At the time of publication of the article, the researchers were inspired by successful superconducting systems containing atoms with tiny nuclei such as lanthanum and yttrium. The researchers wanted to test other elements from the lanthanide group [a group of 15 transition metals, with atomic numbers 57–71, from lanthanum to lutetium], but they concluded that their electronic structures might interfere with the superconducting properties. In particular, they wanted to avoid a half-full electron shell of type 4f, so they chose the element lutetium which contains a full electron shell. In order to mimic the successful performance of the hydrogen sulfide material that the researchers doped with carbon atoms, they tested doping with electron-donating nitrogen atoms.

The researchers first prepared the innovative material in a diamond anvil cell. They placed a 100 micron diameter lutetium foil between the two diamond tips and then surrounded it with a 99:1 hydrogen:nitrogen mixture. They set the pressure to 2 gigapascals and heated the cell in an oven to a temperature of sixty-five degrees Celsius overnight, obtaining a blue-colored substance under normal conditions. As they increased the pressure, the material turned pink when it reached 0.3 gigapascals, at which point it also became a superconductor. When the pressure reached the level of 1 gigapascal the material turned red, and the critical temperature (T_c) below which it became a superconductor reached twenty-one degrees Celsius.    

The nitrogen-condensed lutetium hydride material starts out blue, turns pink as the pressure increases to the point where it becomes a superconductor, then turns red as the pressure increases further. 

[Courtesy: Nathan Dasenbrock-Gammon et al/Springer Nature Limited 2022]

1 GigaPascal is in the range of pressures that researchers use to manufacture chips using a process of "stress engineering" in order to adjust the properties of two-dimensional materials such as graphene, explains the lead researcher. "Now we are in an area where we can practically make use of normal commercially available methods" he adds and says. Although such chips are not yet able to convert electricity, they can be used in the field of quantum computing. In superconducting quantum bits, or qubits, the absence of electrical resistance means that they do not lose information to the surrounding environment in the form of heat. In addition, the electrons contained within superconductors are in a limited number of quantum states that can be controlled by quantum computers and can be measured more simply. Various types of anvil cells can also reach the 1 GPa range while successfully handling slightly larger samples.            

Researcher Eva Zurek from the University of Buffalo in the US is enthusiastic to a limited extent. "If the findings of the study are matched, this work will be particularly exciting and pave the way to the 'holy grail' of superconductivity at moderate pressures and low temperatures," she says. "However, it will be necessary to replicate the experimental results and verify them. Moreover, there are still a number of questions that the researchers will have to answer, including a more accurate characterization of the structure of the superconducting material. The lead researcher of the current study, meanwhile, notes that his research team was able to replicate the findings of the 2020 paper before scientists from the Argonne National Laboratory in Illinois, USA. The team also conducted additional measurements to demonstrate how the innovative material works in front of an audience Live of scientists from Brookhaven National Laboratory. "We compiled all this new data together with the previous data, wrote the latest paper, and submitted same again to the prestigious scientific journal Nature , and it is currently under professional review," says the lead researcher.    

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The news about the research

The crystal structure of the proposed material is nitrogen-condensed lutetium hydride. The hydrogens in the octahedral positions are shown in white and those in the tetrahedral positions in pink. Lutetium atoms are visible in green. [Source: Dasenbrock-Gammon, N. et al, Nature 2023]