It has been over a hundred years since researchers discovered that some materials can conduct electricity perfectly. Such a superconductor could be transformative for science and technology, but all claims of creating one that would work at room temperature and pressure, including recent studies of a material named LK-99, have proven controversial.
Superconductivity was discovered in 1911 when physicist Heike Kamerlingh Onnes noticed that a mercury wire cooled to about -269°C (-452°F) doesn’t resist the flow of electricity. Within a few years materials like lead and alloys of niobium and tin were also found to superconduct at extremely low temperatures, and .
Researchers started to better understand how superconductors work in the 1950s when US physicists John Bardeen, Leon Cooper and John Robert Schrieffer developed a theory for what happens inside of these materials when they are radically cooled. Their so-called BCS theory – short for Bardeen, Cooper and Schrieffer – posited that in superconductors, electrons form pairs in such a way that they can carry electricity without encountering resistance. This crucial electron pairing happens because of vibrations in the lattice of atoms that make up the material, but they stop facilitating it above about -233°C (-387°F).
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BCS theory also earned its authors a , but superconductors seemed possible only with extremely powerful fridges that require pricey liquid helium. This changed in 1987 when researchers discovered a superconductor that contained copper and worked at -196°C (-321°F). Follow-up experiments ultimately bumped superconducting temperatures to -140°C (-220°F).
Currently, superconductors are used to power incredibly strong magnets in particle accelerators and MRI scanners, and they are a building block for quantum computers, which may eventually outperform the world’s best supercomputers. But their impact could be much wider if they didn’t require refrigeration and were easier to handle and manufacture.
Using them for power transmission within the electrical grid would make it more efficient and environmentally friendly and they could also lead to new energy storage devices. Easy-to-use superconducting components could additionally aid the development of more compact, commercially viable fusion reactors.
Why is it so hard to create a room-temperature superconductor?
Part of the difficulty with creating these materials is that neither BCS theory nor any attempts to extend it provide a recipe for creating superconductors that work under different conditions. Researchers have made strides in identifying arrangements of atoms and chemical properties of materials that correlate with superconductivity, but that still leaves an extraordinary number of material combinations to test.
One material of interest is graphene, which is an atom-thin layer of carbon that exhibits a slew of exotic properties, including superconductivity, but is less complicated to make than many copper-containing superconductors. Some experiments show that superconductivity can be controlled as precisely as being able to turn it on and off, by layering and twisting sheets of graphene, but the required temperature for superconductivity is still around -271°C (-456°F).
A , in which researchers crushed a mixture of carbon, sulphur and hydrogen between two diamonds, seemed to provide a new promising possibility. When the diamonds exerted pressure equal to around 70 per cent of that at Earth’s core, the team observed the mixture superconduct at 14°C (57°F). In March of this year, the same team tested a material made from hydrogen, nitrogen and lutetium at a pressure that was scaled down about 155 times and reported superconductivity at the staggeringly warm 21°C (70°F).
Both experiments were scrutinised by other researchers, and the paper that reported the 2020 findings was later retracted. Prior to the retraction some experts in the field questioned . The researchers have stood by their 2023 finding, but a week after announcing the results another team reported that they replicated the experiment and did not detect superconductivity.
In a separate line of research this year, two independent research teams reported finding that superconductors made of scandium work at warmer temperatures when under extreme pressure. But between the results not being well understood theoretically and the difficulty of making the material, how much of a breakthrough this is remains unresolved.
Then just this month another contender entered the scene in the form of a lead, oxygen and phosphorus compound called LK-99. Two papers available on the preprint service arXiv laid out measurements of how this material responds to electricity being pushed through it and being exposed to magnetic fields, which are both cases where it is well known what a superconductor should do. The researchers conducted these tests at room temperature and ambient pressure. They interpreted their measurements to mean that LK-99 does in fact superconduct without having to be cooled or put under pressure.
Their claim was also met with scepticism from the research community. Experts that ¿ìè¶ÌÊÓƵ consulted pointed out features in the data that were either surprising or inconsistent with superconductivity. So, until this work undergoes more rigorous scientific review and is replicated by other research groups, the quest for truly convenient superconductors remains unfinished.
