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A key attribute of a superconductor is its ability to expel magnetic fields and levitate.DOE/SCIENCE SOURCE
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This week, social media has been aflutter over a claim for a new superconductor that works not only well above room temperatures, but also at ambient pressure. If true, the discovery would be one of the biggest ever in condensed matter physics and could usher in all sorts of technological marvels, such as levitating vehicles and perfectly efficient electrical grids. However, the two related papers, posted to the arXiv preprint server by Sukbae Lee and Ji-Hoon Kim of South Korea’s Quantum Energy Research Centre and colleagues on 22 July, are short on detail and have left many physicists skeptical. The researchers did not respond to Science’s request for comment.
“They come off as real amateurs,” says Michael Norman, a theorist at Argonne National Laboratory. “They don't know much about superconductivity and the way they’ve presented some of the data is fishy.” On the other hand, he says, researchers at Argonne and elsewhere are already trying to replicate the experiment. “People here are taking it seriously and trying to grow this stuff.” Nadya Mason, a condensed matter physicist at the University of Illinois, Urbana-Champaign says, “I appreciate that the authors took appropriate data and were clear about their fabrication techniques.” Still, she cautions, “The data seems a bit sloppy.”
A superconductor is a material that can convey an electrical current without any resistance at all. If you’ve ever had an MRI, you’ve lain inside a big electromagnet made of superconducting wire. The resistance-less flow enables it to make a very strong magnetic field without heating up or consuming enormous energy. Superconductors have myriad other uses, from making frequency filters for radio communications to accelerating particles in atom smashers.
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Ordinarily, electrons cannot pass easily through a crystalline solid because they bounce off vibrating atoms in the crystal lattice. However, in some materials, at low enough temperatures, the electrons form loosely bound, overlapping pairs–which can’t be deflected without breaking the pair. And at low temperatures, the vibrations aren’t strong enough to do that. So these electrons glide through the material unimpeded.
Dozens of elemental metals—lead, mercury, niobium, tin—and alloys of them become superconductors when chilled to near absolute zero. In the 1950s, physicists explained how in these conventional superconductors, lattice vibrations also supply the glue that creates the electron pairs. In the 1980s, experimenters identified complex compounds containing layers of copper and oxygen that superconduct at temperatures as high as 133 K. Twenty years later, researchers found that compounds containing layers of iron and arsenic could superconduct at temperatures almost as high. Scientists think these so-called high-temperature superconductors also rely on electron pairing, but created through a different mechanism. Recently, one group has made controversial claims of achieving superconductivity at room temperature—albeit at high pressure—for compounds containing hydrogen, sulfur, and carbon.
Nothing less than the ultimate superconductor. In the preprints, which have not been peer-reviewed, the researchers argue that when seasoned, or “doped” with copper, a material made of the common elements lead, oxygen, and phosphorus superconducts at ambient pressure and temperatures at least as high as 400 K—higher than the boiling point of water. Essentially, they’re saying you can bake up a sample of this stuff, pop it out of the oven, and just sitting there on your lab bench it will conduct electricity without any resistance. They present data that show not only zero resistance, but also that the material appears to expel a magnetic field, a key signature of superconductivity.
There are several, Norman says. First, the undoped material, lead apatite, isn’t a metal but rather a nonconducting mineral. And that’s an unpromising starting point for making a superconductor. What’s more, lead and copper atoms have similar electronic structures, so substituting copper atoms for some of the lead atoms shouldn’t greatly affect the electrical properties of the material, Norman says. “You have a rock, and you should still end up with a rock.” On top of that, lead atoms are very heavy, which should suppress the vibrations and make it harder for electrons to pair, Norman explains.
The papers don’t provide a solid explanation of the physics at play. But the researchers speculate that within their material, the doping slightly distorts long, naturally occurring chains of lead atoms. They say the superconductivity might occur along these 1D channels. But that would be surprising, Norman says, because 1D systems don’t generally produce superconductivity. What’s more, the disorder introduced by the doping ought to further suppress superconductivity. “You have one dimension, which is bad, and you have disorder, which is also bad,” Norman says. Mason isn’t so certain. She notes that Lee and Kim also suggest that a kind of undulation of charge might exist in the chains and that similar charge patterns have been seen in high-temperature superconductors. “Maybe this material really just hits the sweet spot of a strongly interacting unconventional superconductor,” she says.
The big question will be whether anybody can reproduce the observations. That shouldn’t be too hard, Norman says, as lead apatite is a well-known material that others should be able to synthesize. However, doing that isn’t quite as simple as some spectators on social media have made it out to be. “The general public seems oddly pumped about how ‘easy’ the 4-day, multistep, small batch, solid state synthesis is,” Jennifer Fowlie, a condensed matter physicist at SLAC National Accelerator Laboratory, quipped on Twitter. “Some of you haven't had blisters from overusing your pestle and it shows.” Nevertheless, physicists will put the claim to the test very quickly, Norman predicts: “If this is real, we’ll know within a week.”
