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 of mechanical engineers and physicists.
From: University of Rochester
March 8, 2023 – "With
this material, the dawn of ambient superconductivity and applied technologies
has arrived," according to a team led by Ranga Dias, an assistant
professor of mechanical engineering and physics. In a paper in Nature, the
researchers 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
might still seem extraordinarily high (pressure at sea level is about 15 psi),
strain engineering techniques routinely 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 key properties: electrical resistance
vanishes, and the magnetic fields that are expelled pass around the
superconducting material. Such materials could enable:
- Power grids that transmit
electricity without the loss of up to 200 million megawatt hours (MWh) of
the energy that now occurs due to resistance in the wires
- Frictionless, levitating high-speed
trains
- More affordable medical imaging and
scanning techniques such as MRI and magnetocardiography
- Faster, more efficient electronics
for digital logic and memory device technology
- Tokamak machines that use magnetic
fields to confine plasmas to achieve fusion as a source of unlimited power
Previously, the Dias
team reported creating two materials -- carbonaceous sulfur hydride and yttrium
superhydride -- that are superconducting at 58 degrees Fahrenheit/39 million
psi and 12 degrees Fahreneheit/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 unusual lengths to document their
research and head off criticism that developed in the wake of the
previous Nature paper, which led to a retraction by the
journal's editors. The previous paper has been resubmitted to Nature with
new data that validates the earlier work, Dias says. The new data was collected
outside the lab, at the Argonne and Brookhaven National Laboratories in front
of an audience of scientists who saw the superconducting transition live. A
similar approach has been taken with the new paper.
Five graduate students
in Dias's lab -- Nathan Dasenbrock-Gammon, Elliot Snider, Raymond McBride,
Hiranya Pasan, and Dylan Durkee -- are listed as co-lead authors.
"Everyone in the group was involved in doing the experiments," Dias
says. "It was truly a collective effort."
'Startling visual
transformation' at superconductivity and beyond
Hydrides created by
combining rare earth metals with hydrogen, then adding nitrogen or carbon, have
provided researchers a tantalizing "working recipe" for creating
superconducting materials in recent years. In technical terms, rare earth metal
hydrides form clathrate-like cage structures, where the rare earth metal ions
act as carrier donors, providing sufficient electrons that would enhance the
dissociation of the 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 superconductive at temperatures or pressures that are still not
practical for applications.
So, this time, Dias
looked elsewhere along the periodic table.
Lutetium looked like
"a good candidate to try," Dias says. It has highly localized
fully-filled 14 electrons in its f orbital configuration that suppress the
phonon softening and provide enhancement to the electron-phonon coupling needed
for superconductivity to take place at ambient temperatures. "The key
question was, how are we going to stabilize this to lower 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 it hardens the low-frequency optical
phonons, according to Dias. This structure provides the stability for
superconductivity to occur at lower pressure.
Dias's team created a
gas mixture of 99 percent hydrogen and one percent 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
lutetium-nitrogen-hydrogen compound was initially a "lustrous bluish
color," the paper states. When the compound was then compressed in a
diamond anvil cell, a "startling visual 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," Dias says. "I was shocked to see colors of this intensity. We
humorously suggested a code name for the material at this state --
"reddmatter" -- after a material that Spock created in the popular
2009 Star Trek movie." The code name stuck.
The 145,000 psi of
pressure required to induce superconductivity is nearly two orders of magnitude
lower than the previous low pressure created in Dias's lab.
Machine learning
algorithms for predicting new superconducting materials
With funding support
from Dias's National Science Foundation CAREER award and a grant from the US
Department of Energy, his lab has now answered the question of whether
superconducting material can exist at both ambient temperatures and pressures
low enough for practical applications.
"A pathway to
superconducting consumer electronics, energy transfer lines, transportation,
and significant improvements of magnetic confinement for fusion are now a
reality," Dias says. "We believe we are now at the modern
superconducting era."
For example, Dias
predicts that the nitrogen-doped lutetium hydride will greatly accelerate
progress in developing tokamak machines to achieve fusion. Instead of using
powerful, converging laser beams to implode a fuel pellet, tokamaks rely on
strong magnetic fields emitted by a doughnut-shaped enclosure to trap, hold,
and ignite super-heated plasmas. NDLH, which produces an "enormous
magnetic field" at room temperatures, "will be a game-changer"
for the emerging technology, Dias says.
Particularly exciting,
according to Dias, is the possibility of training machine-learning algorithms
with the accumulated data from superconducting experimentation in his lab to
predict other possible superconducting materials -- in effect, mixing and
matching from thousands of possible combinations of rare earth metals,
nitrogen, hydrogen, and carbon.
"In day-to-day
life we have many different metals we use for different applications, so we
will also need different kinds of superconducting materials," Dias says.
"just like we use different metals for different applications, we need
more ambient superconductors for different applications."
Coauthor Keith Lawlor
has already begun developing algorithms and making calculations using
supercomputing resources available through the University of Rochester's Center
for Integrated Research Computing.
An upstate New York hub
for superconducting materials?
Dias's research group
recently moved into a new, expanded lab on the third floor of Hopeman Hall on
the River Campus. This is the first step in an ambitious plan to launch a
degree-granting Center for Superconducting Innovation (CSI) at the University
of Rochester, he says.
The center would create
an ecosystem for drawing additional faculty and scientists to the University to
advance the science of superconductivity. The trained students would broaden
the pool of researchers in the field.
"Our hope is to
make upstate New York the hub for superconducting technology," Dias says.
https://www.sciencedaily.com/releases/2023/03/230308112130.htm
