Superconducting materials are hailed as the “holy grail” of condensed matter physics since their applications are so extensive. From levitating trains and quantum computing to faster and more efficient classical electronics, superconductivity is heavily researched for the swathe of use cases that could transform by vanquishing electrical resistance and magnetic field.
Superconductivity can cause magnetic materials to levitate due to effects on magnetic field lines. Image used courtesy of the University of Rochester
Yet, conventional methods to obtain superconductivity are far from economical, requiring massive amounts of energy and cryogenic cooling. Hence, the next step to achieve affordable and useful superconductivity is to reach superconductivity at higher temperatures (any temperature above 90K (−183°C) in superconductors is considered “high”) with the eventual goal being room temperature.
Some of the top electrical engineering research institutions have published new findings on this goal in the past few months, with achievements hailing from the University of Rochester, MIT, and Yale.
The “World’s First Room-temperature Superconductor”
Instead of achieving superconductivity by means of cooling, the researchers were able to achieve this temperature feat by applying extremely high pressures to a hydrogen-rich material that mimics the lightweight and strong-bond characteristics of pure hydrogen—a strong candidate for high-temperature superconductors.
This material made of yttrium and hydrogen (“yttrium superhydride”), which can be metalized at significantly lower pressures, exhibited a pressure of 26 million pounds per square inch and a record high temperature of 12°F.
The researchers used a diamond anvil cell to test superconducting materials. Image used courtesy of the University of Rochester
According to their article in Nature, the team’s next step was to create a “covalent hydrogen-rich organic-derived material” called carbonaceous sulfur hydride. It was this material that then exhibited superconductivity at 58°F by applying 39 million PSI of pressure.
For this achievement, lead researcher Ranga Dias was announced as a Time100 Next innovator this past week.
MIT Devises a Three-Layer Graphene “Sandwich”
While the University of Rochester’s findings are a significant step forward to reach superconductivity, the high pressures required still limit the feasibility of this technique in the real world. Earlier this month, MIT researchers published a paper that describes a method for obtaining superconductivity at high temperatures without requiring immense pressure.
A 3 layer graphene “sandwich” has shown superconductive behavior at 3K. Image used courtesy of MIT
In 2018, researchers were able to show that when two thin films of graphene are placed on top of one another at a specific angle, the structure actually becomes a superconductor. Since then, the search for more materials sharing this property has proven fruitless—until now.
Now, the same MIT researchers have been able to observe superconductivity in a three-layer graphene “sandwich,” the middle layer of which is twisted at a new angle with respect to the outer layers.
Compared to the original two-layer superconductive material, which has a critical temperature of 1K, the new three-layer material has shown a critical temperature of 3K. As for the exact reason, the scientists are still unsure. “For the moment we have a correlation, not a causation,” the researchers noted in a university press release.
Reimaging Coulomb’s Law for High-temperature Superconductors
More superconductor news emerged from Yale University this month, where researchers published a study that challenges fundamental understandings of electromagnetics in superconductors.
Their study, which was focused on high-temperature superconductors, found that in this state the behavior of electrons does not follow Coulomb’s law. Normally, two electrons typically repel one another, working to move to the place of lowest energy between one another (which is theoretically infinity).
Two equations associated with Coulomb’s law. Image used courtesy of the Physics Hypertextbook
Surprisingly, the Yale researchers found that in high-temperature superconductors, electrons behave independently from other atomic particles, creating a ring-like structure with each other.
This is fundamentally opposed to previous understandings of Coulomb’s law: instead of moving infinitely away from one another, the electrons move close together, forming a ring-like structure. The researchers theorize that this unprecedented effect may be caused by the “underlying functional form of the Coulomb interaction between valence electrons.”
Warming Superconductors Takes Time
While the realities of room-temperature superconductors (beyond a stringent lab setting) are far from a reality, the recent studies from these institutions indicate that researchers are on the right trail.
“History has taught us that a quest like that can take time,” explains superconductor researcher Van der Molen, professor of condensed matter physics at Leiden University. “Kamerlingh Onnes discovered superconductivity in 1911, but it wasn’t until 1957 that a good explanatory theory was published. . . . It’s complicated, even for physicists.”