Art Courtesy of Kara Tao
The world of “Back to the Future,” where levitating hoverboards and cars are the norm, might not be as distant as it appears, thanks to superconductors. That level of prevalence and accessibility, though, hinges upon the discovery of room temperature superconductors. Until now, superconductors have only been found at temperatures far below freezing point. But a few months ago, a potential breakthrough in the discovery of room temperature superconductors was made. Unfortunately, many scientists were skeptical.
Superconductors transmit an electrical current through themselves without losing any energy; in other words, they have no electrical resistance. Additionally, unlike normal conductors, which allow magnetic fields to pass through, superconductors repel external magnetic fields—a property known as the Meissner Effect. This property allows superconducting materials to levitate in the presence of magnets: a macroscopic manifestation of quantum mechanical effects.
With these powerful properties, superconductors have incredible applications. Room-temperature superconductors would allow for lossless electricity transmission over long distances. This could lead to a more efficient and cost-effective electricity distribution in the power grid. And this isn’t just a far-off future. Superconductors are already used in Magnetic Resonance Imaging (MRI) screening technology, which is widely used in the world of medicine. And the Maglev train, a levitating locomotive that can reach speeds of over 250 miles per hour, also relies on superconducting magnets to push it forward.
However, these superconducting properties do not appear naturally. Superconductivity has only been observed when certain materials are held at extremely low temperatures, close to absolute zero (that’s 0 Kelvin, or -273°C). Ever since superconductivity was first discovered back in 1911 by physicist Heike Kamerlingh Onnes, scientists have tried to observe it at the highest temperatures possible. While improvements have been made, these materials must still be kept at extremely low temperatures to express their superconductivity.
Unfortunately, maintaining low enough temperatures to trigger superconductivity is incredibly expensive. Superconductors are so useful that scientists are willing to pay large amounts of money in order to maintain their extremely cold environments. But what if this superconductivity could be triggered at a much higher temperature—say, room temperature? Techniques that were previously limited by exorbitant costs would then become widely available. Furthermore, the scientists who uncovered this secret would be catapulted to international fame with their Nobel-Prize-caliber achievement.
Many scientists have spent years dreaming of this mission: to achieve superconductivity at room temperature and ambient, or standard, pressure. On October 2020, the first instance of a notable advancement in creating a room temperature superconductor was reported by a team led by Ranga Dias at the University of Rochester, and Ashkan Salamat at the University of Nevada. They claimed to have observed superconductivity in a material known as carbonaceous sulfur hydride (CSH) at 288K (15°C). However, this breakthrough came with a condition: it occurred within a diamond anvil cell under immense pressure—approximately 1.5 million times Earth’s atmospheric pressure. Additionally, there were many concerns raised about the processing and analysis of the data presented in the paper.
In light of this, in September 2022, the journal Nature decided to retract the paper. Dias and Salamat claimed again in a second paper published in March 2023 that they had discovered a room temperature superconductor, but this time with lutetium hydride and nitrogen added to the sulfur hydride. They asserted that it had the properties of a superconductor at temperatures of up to 294K (21°C) with much lower pressure. However, this paper was also retracted by Nature on November 7, 2023, following similar concerns with their data.
Sukbae Lee and Ji-Hoon Kim, both physicists from Seoul, South Korea, are yet another duo of scientists who claimed to have achieved this groundbreaking accomplishment. In late July, they published non-peer-reviewed pre-prints of their work, which is common for research scientists. At first glance, their findings were truly groundbreaking. They had discovered a material they named LK-99 that demonstrated all superconductive properties under normal conditions, ostensibly achieving the world’s first room-temperature superconductor.
Researchers worldwide jumped onto this major breakthrough and tried to replicate it. Among the physicists who were reproducing and verifying the experiment was Yuan Li, a condensed matter theorist who leads a research lab at Peking University in China. Li collaborated with two other experimental physicists, providing interpretations of the measurements and observations. “At the beginning, it looked legit. The original authors, they do believe in what they are saying, and they are willing to disclose all the information to the scientific community so that everyone can, in principle, follow their steps and try to verify the observation,” Li said.
Yet when Li and his team began repeating the experiments detailed in the original publication, their data did not support the original claim. Because the scientists claimed that LK-99 had superconductor properties at room temperature, the properties should have been easy to replicate. Yet many physicists and material scientists, including Li, struggled during their replication processes. When testing the levitation of LK-99, Li and his team observed that LK-99 didn’t fully repel the magnet. Instead, one corner of LK-99 touched the magnet, revealing that LK-99 was not levitating, but was still experiencing ordinary attraction to the magnet.
Furthermore, they discovered that its resistance was not actually zero—a critical property of superconductors. With the evidence piling up against LK-99 being a room temperature superconductor, Li and his group published their findings in a scientific journal. It turned out that LK-99, at least at room temperature, was simply a semiconductor with ferromagnetic properties, or high susceptibility to magnetization. Along with papers from other groups that also disproved the original claim about LK-99, Li’s paper helped relegate this highly-anticipated room temperature superconductor as one of science’s many failed attempts.
“This brings light to the high stakes of popular science and the need for competent ‘referees’ to overlook the process,” Li said. Eye-catching research fields like superconductors could potentially revolutionize many industries, so there is naturally a lot more funding for these research projects, but also a lot more pressure to produce tangible results. More pressure for results means a greater likelihood of falsified, or in this case, prematurely published, research. Whether it comes from journal peer-reviewers or fellow scientists, regulation is needed to prevent misinformation or misconceptions from becoming mainstream science.
Despite the failures, Li emphasized the importance of this research. “Although papers were rushed, we should still thank the researchers for their effort and bravery to produce the research. Any information is useful information, thus furthering the story,” Li said.
In the quest to discover a room temperature superconductor, we are reminded to be transparent and skeptical. As Carl Sagan famously said, “Extraordinary claims require extraordinary evidence.” It is not a sign of failure to question extraordinary claims; rather, it is an essential element of the scientific process that ensures the integrity of scientific knowledge. So, while the journey to achieving room temperature superconductivity may still be ongoing, the Sagan Standard serves as a guiding light—reminding us to think boldly, but always demand extraordinary evidence in our relentless pursuit of scientific excellence.