Just weeks after researchers claimed that a material called LK-99 is the world鈥檚 first room-temperature, ambient-pressure superconductor evidence to the contrary has started to pile up. Superconductors conduct electricity perfectly, but studies on LK-99 performed at impressive speed from multiple laboratories dispute that the material has this property.
The search for superconductors has long captured a lot of attention and interest. Because electricity can pass through them without losing energy, they could greatly improve the efficiency of the power grid, lead to new ways to store energy and improve electronic devices overall. However, all known superconductors are impractical for most uses as they only work under extreme conditions like very low temperatures or very high pressures.
So when at the College of William & Mary in Virginia and his colleagues announced that their material, LK-99, superconducts at room temperature and pressure many people 鈥� especially on social media 鈥� responded with excitement and scepticism. A flurry of scientific investigations into LK-99 ensued and now a consensus is emerging that the material, as described by its creators, is very unlikely to be a superconductor after all.
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Across replications experiments, researchers have focused on two properties of LK-99 that could reveal its alleged superconductive nature: its resistivity to electricity and its response to magnetic fields.
By definition, a superconductor has zero electrical resistivity, and Kim鈥檚 team reported this was the case for LK-99 at temperatures ranging from 30掳C (86掳F) to 127掳C (261掳F). But when other teams, like those in , and , made LK-99 they either didn鈥檛 observe zero resistivity at all or only saw it . Some researchers also questioned whether the original measurements were precise enough to distinguish zero resistivity from values too small to be measured by laboratory equipment.
An by at the Chinese Academy of Science and his colleagues indicates that the original zero-resistivity measurement may have been a case of mistaken identity and experimental imprecision. They examined the role of a compound called copper sulphide that was present in the original LK-99 sample, as well as those created by other teams.
Luo and his team found that at around 126掳C (260掳F) 鈥� very close to where initial reports described LK-99 as becoming superconducting 鈥� copper sulphide undergoes a phase transition that makes its resistivity decrease sharply. 鈥淲e believe LK-99 has this phase transition instead of being a superconductor. The electrical resistivity of LK-99 is greatly influenced by the content of the copper sulfide impurity,鈥� says Luo.
On the magnetic fields front, millions of people have now seen videos on social media of LK-99 partially levitating over a magnet, which is an indicator of superconductivity known as the Meissner effect. However, this phenomenon has not been observed consistently across replication experiments and an explanation other than superconductivity could account for it.
at Peking University in China and his colleagues are among those who have and found that it has no special conductivity properties but does respond to a magnetic field in an unusual way.
However, when the researchers measured its magnetic properties more closely, they concluded that the strange behaviour wasn鈥檛 due to the Meissner effect. Rather, the sample had properties more like those of ferromagnetic materials, such as iron. These become magnetised, and therefore attracted to or repelled from some other magnet, when immersed in a magnetic field. Li says that the shape of their sample, which resembled thin flakes, and this property conspired to produce a magnetic torque that pushes LK-99 to 鈥渟tand up鈥� or partially levitate above a magnet.
鈥淚f researchers could discover samples which fully levitate above a magnet, and perhaps even below a magnet, then there must be different reasons other than ferromagnetism for the explanation, but we believe that the kind of 鈥榟alf levitation鈥� we observed has no relation to superconductivity,鈥� he says.
The new experimental evidence, especially with regards to resistivity measurements, makes a compelling case against LK-99 being a superconductor, says at the University of Maryland. 鈥淪omeday we will have room-temperature superconductivity since it is allowed by the laws of physics, but LK-99 does not look like it,鈥� he says.
at the University of Oxford says that 鈥渁ll the signs so far are that this system has some possibly interesting magnetic properties at room temperature, but as most experts suspected, there is no evidence in the replication studies to support the initial claim of room temperature superconductivity.鈥�
She says the explanation for partial levitation by Li鈥檚 team is plausible, but notes that some uncertainty remains when it comes to how similar the samples of LK-99 in replication studies are to the original sample.
Kim has previously told 快猫短视频 that the quality of other researchers鈥� LK-99 samples was behind the initial reports of the absence of superconductivity. He has yet to respond to a request for comment on the experiment from Peking University.
Determining what it means for LK-99 samples to be of high quality has proven controversial and challenging throughout the replication attempts. All the experiments so far have used X-rays to confirm the atoms in the material created are actually arranged how they should be for what Kim and his colleagues called LK-99, however several chemists have raised that this can be imprecise.
This imprecision motivated at Princeton University and her colleagues to focus on copper atoms in LK-99, which Kim and his colleagues said were crucial for the material鈥檚 unusual superconductivity. She says that according to , the procedure for making LK-99 is unlikely to result in these atoms being arranged within the material as initially reported and that this was also evident in the samples that Schoop and her colleagues made by following that procedure.
Their comprehensive calculations of the electrons鈥� properties, which determine how electricity can flow through LK-99, were also discouraging: even when they assumed that the copper atoms were arranged exactly as originally claimed they found results that 鈥渟trongly disfavour high-temperature superconductivity鈥�, says , also at Princeton University, who worked on the project.
None of the researchers that spoke to 快猫短视频 dispute the possibility that some of the original LK-99 samples may have been different enough from those created by the replication efforts to have extraordinary properties. However, those samples or any new measurements of their properties have not been made publicly available, and there are now nearly a dozen follow-up papers looking at different aspects of the claims that tell a similar story 鈥� the chances of LK-99 being a superconductor are looking increasingly slim.
