In a historic achievement, researchers have created a superconducting material at both a temperature and pressure low enough for practical applications.
“With this material, the dawn of ambient superconductivity and applied technologies has arrived,” according to a team led by Ranga Dias, assistant professor of mechanical engineering and physics at the University of Rochester.
In a paper at Natureresearchers describe a nitrogen-doped lutetium hydride (NDLH) that exhibits superconductivity at 69 degrees Fahrenheit and 10 kilobars (145,000 pounds per square inch, or psi) of pressure.
Although 145,000 psi may still seem extremely high (pressure at sea level is about 15 psi), the mechanical deformation techniques commonly used in chip manufacturing, for example, incorporate materials held together by internal chemical pressures that are even higher.
Scientists have been pursuing this breakthrough in condensed matter physics for more than a century. Superconducting materials have two basic properties: the electrical resistance disappears and the repelled magnetic fields pass around the superconducting material. Such materials could enable:
- Electricity networks that carry electricity without losing up to 200 million megawatt-hours (MWh) of the energy that now appears due to resistance in the cables
- Frictionless high speed trains
- More affordable medical imaging and scanning techniques such as magnetic resonance imaging and electrocardiography
- Faster, more efficient electronics for digital logic and memory device technology
- Tokamak machines that use magnetic fields to confine plasma to achieve fusion as a source of unlimited power
Previously, the researchers reported creating two materials—carbonic sulfur hydride and yttrium perhydride—that are superconducting at 58 degrees Fahrenheit/39 million psi and 12 degrees Fahrenheit/26 million psi, respectively, in papers in Nature and Physical Review Letters.
Given the importance of the new discovery, Dias and his team went to extraordinary lengths to document their research and fend off criticism that developed in the wake of the previous one. Nature paper, which led to a retraction by the journal’s editors. The previous document has been resubmitted to Nature with new data validating previous work, according to Dias. The new data was collected outside the lab at Argonne and Brookhaven National Laboratories in front of an audience of scientists who witnessed the superconductivity transition live. A similar approach was taken with the new document.
Five graduate students in Dias’ lab—Nathan Dasenbrock-Gammon, Elliot Snider, Raymond McBride, Hiranya Pasan, and Dylan Durkee—are listed as co-lead authors.
“Everyone on the team was involved in doing the experiments,” says Dias. “It was really a collective effort.”
Hydrides, created by combining rare-earth metals with hydrogen and then adding nitrogen or carbon, have offered researchers a tantalizing “working recipe” for creating superconducting materials in recent years. In technical terms, rare-earth metal hydrides form clathrate-type cage structures, where the rare-earth metal ions act as donors, providing sufficient electrons that would enhance the dissociation of H2 molecules. Nitrogen and carbon help stabilize materials. Bottom line: less pressure is required for superconductivity to occur.
In addition to yttrium, researchers have used other rare earth metals. However, the resulting compounds become superconducting at temperatures or pressures that are still impractical for applications.
So this time, Dias looked elsewhere along the periodic table.
Lutetium seemed “a good candidate to try,” says Dias. It has highly localized fully filled 14 electrons in its orbital configuration that suppress phonon softening and provide the enhancement in electron-phonon coupling required for superconductivity to occur at ambient temperatures. “The key question was how do we stabilize it to reduce the required pressure? And that’s where nitrogen came into the picture.”
Nitrogen, like carbon, has a rigid atomic structure that can be used to create a more stable cage-like lattice within a material and stiffen low-frequency optical phonons, according to Dias. This structure provides the stability for superconductivity to occur at lower pressure.
Dias’ team created a gas mixture of 99% hydrogen and 1% nitrogen, placed it in a reaction chamber with a pure sample of lutetium, and let the components react for two to three days at 392 degrees Fahrenheit.
The resulting lutein-nitrogen-hydrogen compound was initially a “bright bluish color,” the paper says. When the compound was then compressed into a diamond anvil cell, a “shocking optical transformation” occurred: from blue to pink at the onset of superconductivity and then to a bright red non-superconducting metallic state.
“It was a very bright red,” says Dias. “I was shocked to see colors of this intensity. We humorously suggested a codename for the material in this state—“reddmatter”—after a material created by Spock in the popular 2009 Star Trek movie.” The code name stuck.
The 145,000 psi of pressure required to induce superconductivity is almost two orders of magnitude less than the previous low pressure created in Dias’ lab.
Reaching the “Modern Age of Superconductors”
With funding support from Dias’ National Science Foundation CAREER and a grant from the US Department of Energy, his lab has now answered the question of whether superconducting material can exist both at ambient temperatures and at pressures low enough for practical applications.
“A path to superconducting consumer electronics, power transmission lines, transportation and significant improvements in magnetic confinement for fusion is now a reality,” says Dias. “We believe we are now in the modern age of superconductors.”
For example, Dias predicts that nitrogen-doped lutetium hydride will greatly accelerate progress in the development of tokamak machines to achieve fusion. Instead of using powerful, converging laser beams to detonate a pellet of fuel, tokamaks rely on strong magnetic fields emitted from a donut-shaped casing to trap, contain and ignite superheated plasma. The NDLH, which produces a “huge magnetic field” at room temperatures, “will be a game changer” for the emerging technology, Dias says.
Particularly exciting, according to Dias, is the ability to train machine learning algorithms with the accumulated data from superconductor experiments in his lab to predict other possible superconducting materials — in fact, mixing and matching thousands of possible combinations of rare-earth metals, nitrogen. , hydrogen and carbon.
“In everyday life we have many different metals that we use for different applications, so we will also need different kinds of superconducting materials,” says Dias. “Just as we use different metals for different applications, we need more ambient superconductors for different applications.”
Co-author Keith Lawlor has already begun developing algorithms and doing calculations using supercomputing resources available through the University of Rochester’s Center for Integrated Computing Research.
Source: University of Rochester