Featured image credit: US Department of Energy on Flickr
Featured image description: A grey cylinder floating above a white surface. This image demonstrates superconducting levitation
Physics may be on the cusp of revolution. At least, that’s what some Twitter enthusiasts may have you believe—but it could be true, if a recent paper by a research group in Korea has repeatable results. In an age where energy is currency, a discovery like this could have global implications. And the culprits? Lead and copper.
A room temperature superconductor is the holy grail of electronics. It would enable circuits to work without any electrical resistance, meaning that we could power our devices with less energy than we do today. Most superconductors we know and use today require extensive cooling using liquid helium and, more recently, liquid nitrogen, which makes the use of superconductors incredibly expensive.
Researchers Sukbae Lee, Ji-Hoon Kim, Young-Wan Kwon at Korea University made waves with their “poorly-formatted” preprint alleging a that a new material, styled “LK-99” exhibits superconductivity at ambient pressure and at temperatures higher than room temperature. Many were dubious, but the community has nonetheless rushed to recreate their results. So far, there are mixed opinions about the validity of these results, with some suggesting that this LK-99 is just a material with magnetic properties. What the consensus so far seems to be, though, is that it is not a deliberate hoax (as such claims have previously been) and that regardless of the outcome, LK-99 appears to open the door to a new, interesting class of materials.
A brief history
Superconductivity is a rare phenomenon whereby electrical current passes through an object and faces zero resistance. That is to say, electrons flow through a superconductor without colliding with any of the atoms inside the material. Given how densely packed atoms are in solids, it is no surprise that this is rare and happens under very specific conditions. The implications of superconductivity include 100% efficiency in devices, leading to large energy savings. It is currently estimated that around 6% of the energy from power plants is lost due to heat before it even arrives at our homes. In more specialised fields, a room temperature superconductor would slash the costs of running MRI machines and lay the path for physicists developing so-called cold fusion.
The first superconductor, solid mercury, was discovered in 1911 by Dutch physicist Heike Kamerlingh Onnes, who consequently won the Nobel prize in 1913. Mercury is a liquid at room temperature, solidifies at around -38°C, and superconducts only when cooled by liquid helium. Helium is liquid at temperatures below 4.2 Kelvin, which is very close to absolute zero (0 Kelvin) and a similar temperature to the vacuum of outer space itself.
Needless to say, scientists have been striving since then for superconductors that operate at higher temperatures. Helium is rare and expensive to cool; any energy saving due to superconducting tends to be far outweighed by the cooling costs associated with it. So why do people bother using them?
Since they are able to carry larger currents than normal wires, superconductors are fantastic candidates for electromagnets. They generate far higher magnetic fields than we can otherwise achieve, so are essential to the operation of MRI machines and particle colliders such as the LHC in Switzerland. This property is ironic considering that one of the major callsigns of superconductivity is the Meissner effect.
Although they are great at making them, superconductors are not friendly with large magnetic fields. Named after Walther Meissner for his 1933 discovery, the Meissner effect is the expulsion of all magnetic fields from the material. This happens only below what scientists call the critical temperature: the temperature below which the material is superconducting. This happens by strong electrical currents flowing over the surface of the material; the superconductor becomes a strong magnet in order to expel other magnetic fields. This is what causes superconductors to levitate above magnets, an oft-cited visible demonstration of the transition. However, alongside its temperature limitations, a superconductor can only tolerate a certain strength of magnetic field before it “gives up” and transitions back into a somewhat ordinary material. As with many great things in science, superconductivity has thus far been assuaged by caveats that make it useful only in specific circumstances.
The rest of the 20th century saw significant leaps in superconductivity theory in tandem with the discovery of materials boasting ever-increasing transition temperatures. The discovery of superconductors with critical temperatures above 77 Kelvin (the boiling temperature of liquid nitrogen) was enough to earn IBM researchers Bednorz and MĂĽller the Nobel Prize in 1987. Superconductors until today have been considered to be either “Type 1” or “Type 2”, with Type 2 generally having higher transition temperatures, and operating according to a different mechanism. To date (ignoring this recent claim) the highest temperature superconductor that has been found has a critical temperature of -23°C. This material, lanthanum decahydride, can be cooled using dry ice. Superconductivity at this temperature is only achievable if the material is put under immense pressure: 170 Giga Pascals, a pressure on the same order of magnitude as the inner core of Earth.
Too good to be true?
With the above context, the claim of a material that superconducts at ambient pressure and at room temperature far surpasses any research done thus far. This is why materials scientists are rushing to replicate the result in their own labs (and also why most remain cautious).
Some are hopeful, though. Simulations by Sinéad Griffin at Berkeley, University of California indicate that this room temperature-ambient pressure superconductivity is possible , with a tentative explanation for how this superconductivity arises. USA labs have shared via Twitter that they have managed to make the material levitate above a magnet. On August 2nd, Southeast University, China claimed to have found zero resistance at 110 kelvin (close to the current record for ambient pressure) and an overall unique resistance profile. Other labs have demonstrated successful synthesis of the material without finding any extraordinary effects, and another paper has concluded that diamagnetism (another property causing levitation) is unlikely to occur in the material without superconductivity also being present.
LK-99 was developed in 1999 by Korean researchers Sukbae Lee and Ji-Hoon Kim; groups have been studying the properties of the material for decades. The uploading of a paper draft to preprint website ArXiv, after two failed patent attempts, has sparked this most recent craze. The field of room temperature superconductivity has been plagued with hoaxes and false results, much like the study of alchemy in the past. It is this background against which materials scientists work; any claim of this nature is bold and hence fodder for intense scepticism.
Experts are divided on whether this premature upload and consequent rush is a good thing for the scientific community. Journals such as Nature operate under a peer-review basis—that is, for a paper to get published, usually other parties have tried to replicate the research and verified it. This has not stopped hoaxes from slipping through the cracks, however. The hype surrounding LK-99 has sparked a large volume of new papers in a short time frame, and with it, plenty of online misinformation. It remains to be seen whether LK-99 is a turning point not only for materials research, but also for the way science itself is done.
Overall, results remain broadly inconsistent, and theoreticians claim that the synthesis of LK-99 is difficult and unpredictable. Due to the complexity of the process and the potential new physics involved, it may be some months before scientists know the truth about LK-99.
Interested readers may follow developments on Wikipedia.
