Compressing simple molecular solids with hydrogen at extremely high pressures, University of
Rochester engineers and physicists have, for the first time, created material that is superconducting
at room temperature.
Featured as the cover article in the journal Nature, the work was conducted by the lab
of Ranga Dias, an assistant professor of mechanical engineering and of physics and astronomy.
Ranga Dias says developing materials that are superconducting—without electrical resistance
and expulsion of magnetic field at room temperature—is the “holy grail” of condensed matter physics.
In setting the new record, Dias and his research team combined hydrogen with carbon and sulfur
to photochemically synthesize simple organic-derived carbonaceous sulfur hydride in a diamond anvil
cell, a research device used to examine miniscule amounts of materials under extraordinarily
high pressure.
The carbonaceous sulfur hydride exhibited superconductivity at about 58 degrees Fahrenheit
and a pressure of about 39 million pounds per square inch (psi).
Because of the limits of low temperature, materials with such extraordinary properties
have not quite transformed the world in the way that many might have imagined.
However, this new discovery will break down these barriers and open the door to many potential
applications, such as 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,
A new way to propel levitated trains and other forms of transportation, Medical imaging and
scanning techniques such as MRI and magnetocardiography, and Faster, more efficient electronics for
digital logic and memory device technology.
The amount of superconducting material created by the diamond anvil cells is measured in
picoliters—about the size of a single inkjet particle.
The next challenge, is finding ways to create the room temperature superconducting materials
at lower pressures, so they will be economical to produce in greater volume.
In comparison to the millions of pounds of pressure created in diamond anvil cells, the
atmospheric pressure of Earth at sea level is about 15 psi.
First discovered in 1911, superconductivity gives materials two key properties.
Electrical resistance vanishes.
And any semblance of a magnetic field is expelled, due to a phenomenon called the Meissner effect.
The magnetic field lines have to pass around the superconducting material, making it possible
to levitate such materials, something that could be used for frictionless high-speed
trains, known as maglev trains.
Powerful superconducting electromagnets are already critical components of maglev trains,
magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) machines, particle
accelerators and other advanced technologies, including early quantum supercomputers.
But the superconducting materials used in the devices usually work only at extremely
low temperatures—lower than any natural temperatures on Earth.
This restriction makes them costly to maintain—and too costly to extend to other potential applications.
Previously, the highest temperature for a superconducting material was achieved last
year at the Max Planck Institute for Chemistry in Mainz, Germany, and at the University of
Illinois at Chicago.
That team reported superconductivity at -10 to 8 degrees Fahrenheit using lanthanum superhydride.
Researchers have also explored copper oxides and iron-based chemicals as potential candidates
for high temperature superconductors in recent years.
However, hydrogen—the most abundant element in the universe —also offers a promising
building block.
To have a high temperature superconductor, stronger bonds and light elements are the
two very basic criteria.
Hydrogen is the lightest material, and the hydrogen bond is one of the strongest.
Solid metallic hydrogen is theorized to have high Debye temperature and strong electron-phonon
coupling that is necessary for room temperature superconductivity.
However, extraordinarily high pressures are needed just to get pure hydrogen into a metallic
state.
And so, Dias’s lab at Rochester has pursued a “paradigm shift” in its approach, using
as an alternative, hydrogen-rich materials that mimic the elusive superconducting phase
of pure hydrogen, and can be metalized at much lower pressures.
First the lab combined yttrium and hydrogen.
The resulting yttrium superhydride exhibited superconductivity at what was then a record
high temperature of about 12 degrees Fahrenheit and a pressure of about 26 million pounds
per square inch.
Next the lab explored covalent hydrogen-rich organic-derived materials.
This work resulted in the carbonaceous sulfur hydride.