A paper published in the 2023-03-08 issue of Nature reports “Evidence of near-ambient superconductivity in a N-doped lutetium hydride”. (The full text is behind a Springer paywall that wants US$ 39.95 for a PDF or US$ 9.99 to “rent” it for 48 hours. The paper has not yet appeared on Sci-Hub.) Here is the abstract:
The absence of electrical resistance exhibited by superconducting materials would have enormous potential for applications if it existed at ambient temperature and pressure conditions. Despite decades of intense research efforts, such a state has yet to be realized. At ambient pressures, cuprates are the material class exhibiting superconductivity to the highest critical superconducting transition temperatures (T_c), up to about 133 K. Over the past decade, high-pressure ‘chemical precompression’ of hydrogen-dominant alloys has led the search for high-temperature superconductivity, with demonstrated T_c approaching the freezing point of water in binary hydrides at megabar pressures. Ternary hydrogen-rich compounds, such as carbonaceous sulfur hydride, offer an even larger chemical space to potentially improve the properties of superconducting hydrides. Here we report evidence of superconductivity on a nitrogen-doped lutetium hydride with a maximum T_c of 294 K at 10 kbar, that is, superconductivity at room temperature and near-ambient pressures. The compound was synthesized under high-pressure high-temperature conditions and then—after full recoverability—its material and superconducting properties were examined along compression pathways. These include temperature-dependent resistance with and without an applied magnetic field, the magnetization (M) versus magnetic field (H) curve, a.c. and d.c. magnetic susceptibility, as well as heat-capacity measurements. X-ray diffraction (XRD), energy-dispersive X-ray (EDX) and theoretical simulations provide some insight into the stoichiometry of the synthesized material. Nevertheless, further experiments and simulations are needed to determine the exact stoichiometry of hydrogen and nitrogen, and their respective atomistic positions, in a greater effort to further understand the superconducting state of the material.
Here is an illustration liberated from the paper and posted on Twitter which appears to show superconductivity at room (20° C) temperature with a compression of “only” 10 kilobar (1 gigapascal), or 10,000 times atmospheric pressure, but it’s a big improvement over the previous record holder which exhibited superconductivity at −13° C and 190 gigapascals temperature.
Some superconductivity researchers are applauding the result as a breakthrough, while others caution “Not so fast”, as described in the Quanta Magazine article, “Room-Temperature Superconductor Discovery Meets With Resistance”.
While the announcement has been greeted with enthusiasm by some scientists, others are far more cautious, pointing to the research group’s controversial history of alleged research malfeasance. ([co-author] Dias strongly denies the accusations.) Reactions by 10 independent experts contacted by Quanta ranged from unbridled excitement to outright dismissal, with many of the experts expressing some version of cautious optimism.
“If it turns out to be correct, it’s possibly the biggest breakthrough in the history of superconductivity,” said James Hamlin, a physicist at the University of Florida who was not involved in the work. If it’s true, he said, “it’s an earth-shattering, groundbreaking, very exciting discovery.” But incidents involving the team’s previous work — including but not limited to a near-room-temperature superconductivity claim published in Nature in 2020 and retracted late last year — have cast a shadow across today’s announcement. “It’s hard to not wonder if some of the same problems that have gone unaddressed in previous work also exist in the new work,” Hamlin said.
“I am really excited to see the result. And I don’t in any way doubt that what they’re observing is what it is,” said Siddharth Saxena, a physicist at the University of Cambridge who was not involved in the new work. Eva Zurek, a theoretical chemist at the University at Buffalo who often communicates with the Rochester group but who was also not involved in the research, said that a material that superconducts under these conditions “would impact every aspect of our life in ways we cannot imagine.” Hamlin agrees that the demonstration “is a tour de force of every kind of measurement you would want to see on this material, producing exactly the type of data you would hope to see.”
“There is a lot of evidence for superconductivity here if you take it at face value,” said Jorge Hirsch, a physicist at the University of California, San Diego. “But I do not believe any of what these authors say. I am not sold at all.”
Hirsch said his mistrust stems from a long history of allegations of research malfeasance made against previous and current members of the group, many of which he has pressed. Most recently, in 2020 Dias and his co-authors published a study of a carbonaceous sulfur hydride (CSH) that hit its critical transition at around 14 degrees Celsius (57.2 degrees Fahrenheit) and 267 gigapascals. Almost immediately, a handful of experts spotted unusual patterns in the data used to verify the material’s response to magnetic fields. When Dias and his frequent collaborator, Ashkan Salamat, a physicist at the University of Nevada, Las Vegas released their raw data a year later in the form of a 149-page document, they detailed an unusual and complicated method for eliminating background magnetic interference — one they said was necessary for them to detect the tiny magnetic field rejected by the small sample. This method was inconsistent with how they’d described the procedure in the original paper, which led Nature to issue a retraction last September.
Hirsch and other physicists allege that the misconduct goes beyond a misleading mix-up regarding the magnetic background. In September, Hirsch and Dirk van der Marel, a professor emeritus at the University of Geneva, published a claim that what Dias and Salamat had released as raw CSH data was actually derived from the published data. “[We] proved basically mathematically that the raw data are not measured in the laboratory; they are fabricated,” Hirsch said. Hamlin independently released a preprint last October claiming that the electrical resistivity data also appeared to have been processed in an undisclosed manner — a new allegation atop the issue that led to the 2022 retraction.
However, outside access may fall short of the community’s hopes. Dias and Salamat have founded a startup, Unearthly Materials, which, Dias said, has already raised over $20 million in funding from investors including the CEOs of Spotify and OpenAI. They’ve also recently applied for a patent on the lutetium hydride material, which would deter them from mailing out samples. “We have clear, detailed instructions on how to make our samples,” Dias said. “We are not going to distribute this material, considering the proprietary nature of our processes and the intellectual property rights that exist.” He suggested that “certain methodologies and processes” are also off the table.
What’s what I hear … a warning bell? We’ll see….