@jinpa said in Scientific Science:
@BernieTheBernie said in Scientific Science:
and a comment on that topic in Science:
https://www.science.org/content/article/something-seriously-wrong-room-temperature-superconductivity-study-retractedIt's pay-walled, so a summary or extract would be appreciated.
It seems to be additional info for the Nature article. These seem to be the relevant bits but there is more in there:
The retraction comes even as excitement builds for the class of superconducting materials called hydrides, which includes the carbonaceous sulfur hydride (CSH) developed by Dias’s team. Under pressures greater than at the center of the Earth, hydrogen is thought to behave like a superconducting metal. Adding other elements to the hydrogen—creating a hydride structure—can increase the “chemical pressure,” reducing the need for external pressure and making superconductivity reachable in small laboratory vises called diamond anvil cells. As Lilia Boeri, a theoretical physicist at the Sapienza University of Rome, puts it, “These hydrides are a sort of realization of metallic hydrogen at slightly lower pressure.”
In 2015, Mikhail Eremets, an experimental physicist at the Max Planck Institute for Chemistry, and colleagues reported the first superconducting hydride: a mix of hydrogen and sulfur that, under enormous pressures, exhibited a sharp drop in electrical resistance at a critical temperature (Tc) of 203 K (–70°C). That was nowhere near room temperature, but warmer than the Tc for most superconducting materials. Some theorists thought adding a third element to the mix would give researchers a new variable to play with, enabling them to get closer to ambient pressures—or room temperatures. For the 2020 Nature paper, Dias and colleagues added carbon, crushed the mix in a diamond anvil cell, and heated it with a laser to create a new substance. They reported that tests showed a sharp drop in resistance at a Tc of 288 K (15°C)—roughly room temperature—and a pressure of 267 gigapascals, about 75% of the pressure at the center of the Earth.
But in a field that has seen many superconducting claims come and go, a drop in resistance alone is not considered sufficient. The gold standard is to provide evidence of another key attribute of superconductors: their ability to expel an applied magnetic field when they cross Tc and become superconducting. Measuring that effect in a diamond anvil cell is impractical, so experimentalists working with hydrides often measure a related quantity called “magnetic susceptibility.” Even then they must contend with tiny wires and samples, immense pressures, and a background magnetic signal from metallic gaskets and other experimental components. “It’s like you’re trying to see a star when the Sun is out,” Hamlin says.
The study’s magnetic susceptibility data were what led to the retraction. The team members reported that a susceptibility signal emerged after they had subtracted a background signal, but they did not include raw data. The omission frustrated critics, who also complained that the team relied on a “user-defined” background—an assumed background rather than a measured one. But Salamat says relying on a user-defined background is customary in high-pressure physics because the background is so hard to measure experimentally."