Room-Temperature Superconductors: Why Scientists Are Still Searching for This ‘Holy Grail’
Improving the technology of superconductors, already used in the Large Hadron Collider and MRI machines, would revolutionize our everyday life. Here’s how.
You are viewing a single comment's thread from:
Electricity powers the modern world—unfortunately, it’s pretty inefficient.
Some 700,000 circuit miles of transmission lines and another 5.5 million miles of distribution lines make up the U.S. electric grid, but those aluminum and copper wires, while being extremely good conductors, are far from perfect. Because electric current meets some small measure of resistance while traveling through those wires, lots of energy is lost as heat. According to the National Defense Research Council, five percent of the energy produced in the U.S. is completely wasted during this electrical journey. While that may seem like a small slice of the electron pie, that’s enough juice to power all of central America four times over.
But the electric grid is only one (albeit big) example of wasted energy—anything that requires electricity to function similarly wastes energy in this way. And according to physics, that’s just the way it has to be. Or is it?
Turns out, a very peculiar thing happens when metals, alloys, and other materials get cold, like approaching absolute zero cold: electrical resistance disappears. Science defines these as superconductors, a large family of diverse materials that underpin some of the most advanced technologies in the world.
“This is the promise of superconductors,” Nadya Mason, a condensed matter physicist at the University of Illinois Urbana-Champaign, tells Popular Mechanics. “Superconductors are the materials where electrons can move through the material without losing energy as heat … but the problem with superconductors so far is that they only work at extremely low temperatures.”
Because of these bone-shattering temperatures, superconductors are mostly relegated to advanced technologies. But what if science could somehow find a material that performed this atomic superconducting dance at room temperature?
“Any metal in principle can be a superconductor … [but] people are interested in finding new materials where the transition temperature, where the material goes superconducting, is higher and higher,” Richard Greene, a condensed matter physicist and founding director of the Center for Superconductivity Research at the University of Maryland, tells Popular Mechanics. “There’s always been the hope of making a room-temperature superconductor, it’s sort of a holy grail.”
And like a modern-day Sir Galahad, researchers from South Korea believe that search is over, publishing two papers in July 2023 detailing a new material that’s supposedly a superconductor at room temperature and ambient pressure. But despite the viral sensation of this so-called “discovery,” experts in the field aren’t so certain, and efforts to replicate LK-99, the supposed room-temperature superconductor, have failed.
To fully understand this scientific drama, let’s talk about superconductors: their history, their structure, and their incredible potential.
Mercury Practically Zero”
Humans have known about electricity for thousands of years, but it wasn’t until the turn of the 20th century when scientists finally discovered one of its most puzzling attributes. This millennia-long delay, in part, was because humans had no way of simulating temperatures approaching absolute zero, or -459.67 degrees Fahrenheit.
That changed on April 8, 1911, when Dutch physicist Heike Kamerlingh Onnes, while experimenting with liquid helium, plunged the metal Mercury all the way down to just 3 Kelvin. With his assistant soon shouting “zero, zero, still zero!” from a nearby room, Kamerlingh Onnes jotted in his notebook, “mercury practically zero,” a reference to the metal’s complete lack of electrical resistance.
He didn’t know it at the time, but the Dutch scientist had just discovered an entirely new field of physics, a feat that would earn him the Nobel Prize in 1913. It’s from this moment that the era of superconductors truly began.
“[Superconductivity] is an amazing phenomenon, and it took about 50 years before they figured out how it works,” Greene says. “You actually need to understand quantum mechanics—you can’t understand it using classical physics.”
That leap in understanding arrived in 1957, when three physicists from the University of Illinois—John Bardeen, Leon Neil Cooper, and John Robert Schrieffe—developed the BCS theory (named after their last initials) to describe all the quantum goings-on when a metal becomes a superconductor at critical temperature, or Tc (which varies by material).
The theory goes that negatively charged electrons, which would usually repel each other under normal circumstances, actually form pairs (known as “cooper pairs”) when cooled down to Tc. This pairing is effectively created by electron interactions with vibrations, or “phonons,” in the atomic crystalline structure. The result? Zero electrical resistance.
“These electrons pair up over distances that are larger than the scale at which they’d be hitting atoms,” Mason says. “So if you imagine a road that has a lot of bumps in it, [electron pairs] lift themselves up above the road … so that the bumps are irrelevant to them.”
Superconductors also have unique magnetic properties, as they naturally expel magnetic fields while simultaneously creating eddy currents of their own. This is what’s known as the “Meissner effect,” and it explains why levitation is often regarded as an effect of superconductivity (though it can be caused by other means).
In 1933, German physicists Walther Meißner (anglicized “Meissner”) and Robert Ochsenfeld discovered a strange habit of superconductors. When materials were cooled to their transition temperature, they expelled magnetic fields. This was true when a substance was cooled in the presence of magnetic fields or applied after the fact.
“If you try to change the magnetic field through a metal, a current will be induced in that metal and will try to oppose the change in that magnetic field,” Greene says. “When the material goes superconducting and the magnetic field is expelled, that’s a change in the magnetic field. Normally, that current would die out because the metal has resistance … but if you have a superconductor, then there’s no resistance anymore, so the current stays there forever.”
This induced diamagnetism—magnetic field repulsion—is why levitation is a tell-tale sign of a superconductor, but if you induce a strong enough magnetic field (a specific threshold known as “critical field”), the material will stop being superconductive. However, it’s worth noting that other effects can also cause levitation (which is why you can buy a variety of levitating desk toys on Amazon).
Although you can induce superconductivity by changing the atomic structure with increased pressure, the big secret to this electron magic trick is temperature. Because temperature is essentially just energy by another name, it brings with it thermal excitations that disrupt these paired electrons, Mason says. So for a material to be a superconductor, that thermal energy must be lower than the paired electrons’ energy. That’s why superconductors usually occur at temperatures approaching absolute zero, when such thermal energy is extremely low.
Emphasis on the word “usually.”
Things Start Warming Up
So far, this has all been a standard description of superconductors—the kind of stuff that had Kamerlingh Onnes scratching his head back in 1911. But the term “superconductor” is really an umbrella term for a variety of materials that can achieve superconductivity in a variety of ways.
Some materials—known as s-wave, d-wave, p-wave, and recently g-wave superconductors—are categorized by how two electrons specifically pair up in the first place. Other superconductors use entirely different mechanisms that don’t require phonons at all, or react to magnetic fields in different ways (Type I and Type II superconductors), and some even reach Tc at temperatures scientists once thought impossible.
“Based on the [BCS] theory, it was thought that nothing could superconduct above 40 Kelvin,” Greene says. “That idea was completely destroyed in the 1980s when a new material was discovered: copper oxides.”
These new materials, such as the ceramic known as yttrium barium copper oxide, became a superconductor at 93 Kelvin—still cold, but not absolute-zero cold. But maybe even more importantly, these materials were the first superconductors above the boiling point of liquid nitrogen, which is cheaper and easier to handle than liquid helium. Today, the highest-temperature superconductor under ambient pressure is around 130 Kelvin, or -225 degrees Fahrenheit.
Even at these low temperatures and high pressures, superconductors have found their way into a variety of world-changing technologies, mostly through superconducting wires that create powerful electromagnets. CERN’s Large Hadron Collider, the largest particle accelerator in the world, uses superconducting electromagnets to “bend and tighten” a particle’s trajectory; and the ITER tokamak, the most advanced fusion reactor on the planet, will contain the most integrated superconducting magnet system ever built when it goes online in 2025. But the most ubiquitous use of superconductors is in magnetic resonance imaging (MRI) machines, which leverage superconducting electromagnets to glimpse the human body in unprecedented detail.
While these inventions are certainly miraculous, they are still cumbersome as these materials constantly require ultra-cool temperatures (usually in the form of expensive liquid helium)—not exactly something that can feasibly cover the millions of miles of cable that make up the U.S. electric grid.
But if science could somehow discover a material that acts at a superconductor at room temperature, our electric world would enter an entirely new era.
New Era or False Start?
The history of electricity is punctuated with many major moments. Michael Faraday’s discovery of electromagnetic induction, James Clerk Maxwell’s famous equations, Nikola Tesla’s creation of an A/C induction motor, and Bell Labs’ invention of the transistor have all earned a top spot—and the discovery of a room-temperature superconductor would surely be their equal.
“Even though the mechanism may not be known and even though people are still trying to understand high-temperature superconductors, there’s no physics reason why we can’t have a room-temperature superconductor,” Mason says. “The application possibilities would broaden tremendously if we had [one].”
It’s this immense promise (and likely a guaranteed Nobel Prize) that’s caused some furor in condensed-matter physics in recent years. Paper after paper claims to have found this elusive, superconducting White Whale, only for those hopes to be dashed along the rocky shores of reality.
Claims of room-temperature superconductivity date back to at least the year 2000, though many of them require immensely high pressures. A high-profile dud in recent memory came in October 2020, when a physicist from the University of Rochester in New York published a paper in the journal Nature announcing the discovery of a superconducting material at 59 degrees Fahrenheit (albeit under extreme pressure). The work captured tons of headlines, but Nature retracted the paper two years later after physicists failed to reproduce the results, citing “data-processing irregularities.”
But the newest—and most perplexing—candidate comes from a team of South Korean researchers, who in two separate papers detail the properties of a material they call “LK-99”, a lab-made material containing lead, oxygen, phosphorus, and sulfur. According to the paper, LK-99 showcases tell-tale signs of the Meissner effect (it levitates) and it is supposedly a superconductor with a Tc of 260 degrees Fahrenheit at ambient pressure, meaning it can basically operate in any environment on Earth.
This non-peer-reviewed preprint, boldly titled “The First Room-Temperature Ambient-Pressure Superconductor,” ignited a firestorm last month—both online and in physics departments around the world—as experts and laboratories rushed to recreate the material and reproduce these amazing results. But even from the very beginning, most condensed-matter physicists, including Mason and Greene, were skeptical.
“Even though they’ve shown levitation and resistance versus temperature curves in their paper … none of those measurements seem to have the reliability that a typical paper reporting superconductivity would have,” Greene says. “For example, one of the papers shows electrical resistance versus temperature, and when it comes to superconductivity there’s a very sharp drop in the resistance … the drop is much too sharp. It wouldn’t happen that quickly.”
Greene and Mason also mention some graph inconsistencies that make it hard to discern if this material is even a superconductor at all.
“I think one thing that’s exciting about this paper is that they were very clear about how they made the material. It’s a material that many people can make and reproduce,” Mason says, but he also points out a few red flags. “The resistivity plot is troublesome to me … if you took their plot of a superconductor, and just put gold on the same plot, gold would look like there was also zero resistance.”
At first, for every validation study that showed promising results, another study took the wind out of Ahab’s metaphorical sails. Finally, two weeks after its arrival, the International Center for Quantum Materials—an influential Chinese superconductor lab—confirmed that LK-99 wasn’t a superconductor at all, but instead displayed a kind of ferromagnetism.
So for now, the dream of room-temperature superconductors is on pause. But despite LK-99’s unfortunate fate, the dream has never been so tantalizing.