Controversy over room temperature superconductors: growing doubts about an alleged breakthrough in superconducting physics

Wrong data? In 2020, researchers were able to make a superconducting material at room temperature for the first time, at least that’s what they reported. But now doubts about this goal are growing and “Nature” has withdrawn its specialist article. The reason for this is the undocumented processing of the magnetic field data, but also problems in reproducing the experiment. Since then, authors and critics have debated whether superconductivity has been demonstrated at room temperature or not.

Common high-temperature superconductors need low negative temperatures to become resistance-free conductors. Because only then do their electrons take on the states that allow them to move without resistance in the material. In recent years, however, physicists have discovered a class of materials that become superconducting under high pressure even at mild temperatures: metal hydrides. Lanthanum hydride loses its strength at minus 23 degrees and hydrogen sulfide at minus 70 degrees.

In October 2020, the magazine “Nature” ran a sensation on the front page: a team led by Ranga Dias of the University of Rochester in New York had managed to make a superconducting hydride at plus 15 degrees, almost at room temperature. While this also required the immensely high pressure of 275 gigapascals, an important breakthrough seemed to have been achieved: the first superconductivity at room temperature.

Suspicious magnetic data

But in the meantime doubts about this result and about the honesty of the physicists team increase. The debate is not ignited by the drop in electrical resistance clearly demonstrated in the experiment, but by the data on the magnetic behavior of sulfur, carbon and hydrogen hydride. In addition to lossless electrical conduction, the main feature of true superconductivity is also a shielding effect against external magnetic fields.

Although Dias and his team presented data on this magnetic behavior in their article, they have been heavily modified. According to this, the decisive signal appeared only after a “background signal” had been subtracted. However, neither the data for this background nor the raw data have been published. Nature magazine withdrew the article in September 2022 due to mounting criticism of this procedure. Motivation: The researchers used a non-standard custom technique and did not disclose the details in the article.

Raw data does not match the card

In response to criticism, Dias and one of his colleagues subsequently sent the raw data from their experiment as prepress. However, upon closer analysis, physicists Jorge Hirsch of the University of California at San Diego and Dirk van der Marel of the University of Geneva also question these data. Your accusation: the raw data published later do not correspond to the paper published in “Nature”. According to the researchers, they cannot therefore come from the same experiment.

Dias and a team defend themselves against these accusations and, in turn, accuse Hirsch of having carried out a personal revenge. In fact, Hirsch was temporarily banned from the arXiv prepress platform due to his ongoing attacks on slides and co. He is also known as a strong critic of superconducting hydrides. “We remain true to our work, it has been verified experimentally and theoretically,” Dias told Science.

Playback not yet successful

However, Hirsch is not the only physicist to have expressed doubts about the procedure used by Dias and his team and the raw data subsequently published. “This raises more questions than answers,” explained Brad Ramshaw of Cornell University in a recent publication in Science. To make matters worse, the experiment so far has not been able to be reproduced by other teams. Mikhael Eremets of the Max Planck Institute for Chemistry in Mainz, who studied hydrogen sulfide as a high-pressure superconductor, also failed, not least because some basic information on the procedure was missing.

Whether the room temperature superconductor actually exists remains an open question for the moment. However, there appears to be a general consensus among solid-state physicists that hydrides and even hydrides with a mixture of carbon could be a promising approach for new high-temperature superconductors. (Retraction of nature, matter and radiation to extremes, 2022; doi: 10.1063 / 5.0088429)

Source: Science, Nature

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