The following piece offers a brief history of “room-temperature semiconductors.” It’s a “hot” topic in science world at the moment, so we thought we’d better get someone to explain it for us.
That someone is Joanna Thompson, who writes about science (and nature) for a number of leading journals, including Quanta magazine, Scientific American and Audubon magazine. Closer to home, she’s the science editor of News Items.
Here is her report:
Over the last couple of weeks, you may have encountered a viral video of a small floating rock that took the internet by storm. The pebble is hovering above a material called LK-99. In a July 22 preprint paper, a team of South Korean researchers claim that this copper-and-lead crystal is the zenith of condensed matter physics: a room-temperature superconductor.
It’s a bold assertion – and, unfortunately, it appears to be bunk. In the days following the preprint's publication, a number of labs, including Lawrence Berkeley National Labs, China's Huazhong University of Science and Technology and the University of Manchester in the UK, rushed to synthesize their own LK-99 samples. None of them observed flawless superconductivity in the material. In fact, the latest evidence from the National Physical Laboratory of India suggests that LK-99 is not only not a superconductor, but that it might be anti-superconducting, becoming more resistive at lower temperatures.
False alarms are nothing new in the world of room-temperature superconductors. They have a long scientific shadow, stuffed with hearsay, hope, near-misses and outright lies. What follows is a brief history of the science and its enduring appeal.
Researchers discovered the first superconductive material over a century ago. In 1911, Dutch physicist Heike Kamerlingh Onnes happened upon a material, solid state mercury, that had the power to conduct electricity with absolutely no resistance, allowing 100% of its energy to pass through. It was a technological breakthrough with the potential to unlock perfect efficiency in electronic devices and bring to life a myriad of science fiction technologies, from hoverboards to eternal batteries to personal quantum computers.
But the problem with materials like mercury is that they only superconduct under extremely low temperatures (think -450 °F) or extremely high pressures. Obviously, this poses a challenge for using them outside of a lab setting. Room-temperature and -pressure superconductors have become something of a holy grail for physicists, sort of like cold fusion and zero-point energy. Unlike cold fusion and zero-point energy, however, pretty much the entire scientific community agrees that ambient condition superconductors are physically possible. It’s just a matter of time before someone strikes gold (and gold might be a component).
1986 was the first year that scientists came tantalizingly close. Researchers from IBM discovered a material capable of superconducting at a balmy -292°F, proving that zero-resistance electrical flow was possible above the temperature of liquid nitrogen. The breakthrough sparked a new age in so-called "high temperature" superconductivity research. But it also ushered in a host of frauds.
In the early 2000s, South African researcher Johan Prins claimed that he’d accidentally discovered ambient superconductivity in oxygen-doped diamonds. His paper was swiftly dismissed for making no sense. Around the same time, another group made a similar claim for palladium hydride, though their work has never been reproduced. A 2012 paper put forth graphite as a yet another unconfirmed room-temperature superconducting candidate. And in 2019, the US military filed a patent on a room-temperature superconductor that, as far as anyone knows, doesn’t actually work.
Some of these claims are lighthearted fun. In the early days of the Covid pandemic, a couple of presumably bored physicists published an April 1st preprint describing how they’d achieved room-temperature superconductivity: by simply cooling the room down to -450 °F.
But others are downright scandalous. A 2018 paper from a group of Indian scientists was dismissed when a reviewer noticed that they had forged most of their magnetic field data. And earlier this year, physicist Ranga Dias — who published two separate papers describing room-temperature superconductors — was revealed to have plagiarized much of his research.
All these phony claims beg the question: Why go through all the trouble of claiming that you’ve manufactured a room-temp superconductor if you haven’t?
Unfortunately, the most likely explanation is also the simplest: funding. Grants in science are hard to come by, especially in the more esoteric areas of physics. To snag any significant federal money, a lab has to show not only impressive results, but results that also have practical, real-world applications. Creating a superconductor that works at ambient temperature and pressure is one of the most tantalizing possible pieces of grant-bait. Even if the claim only holds up for a couple of years, any reputable lab that produces a paper to that effect will secure a substantial slice of the funding pie. And it’s worth noting that five of the last twenty-two Nobel prizes in physics have been awarded for superconductivity-related research.
This does not mean that every disproven room-temperature superconductivity claim is blatant fraud. Though it may sound straightforward, superconductivity can be quite difficult to detect. There isn’t one specific measurement that scientists need to take; it’s more of an aggregate of material properties, including the ability to levitate other materials (the Meisser effect), its critical current and single-particle tunneling gaps, among others. These properties exist independently in materials that aren’t superconductive, so observing one or two doesn’t automatically spell jackpot. And Meisser levitation can be easily confused with other strong magnetic effects, such as diamagnetism. Some of the scientists who prematurely published about room-temperature superconductors may have discovered a legitimately neat new material and gotten swept up in the excitement when it displayed one of these attributes.
For now, it seems that LK-99 joins the ranks of room-temperature superconductor candidates that didn't live up to the hype. The search for the holy grail of condensed matter physics, however, continues. The belief that it will be found never dies.