No miracles! The LK-99 superconductor dream is over

Before moving on to LK-99, I think it is necessary to start with some information in order to have some general knowledge. In 1911, Dutch physicist Heike Kamerlingh Onnes discovered that the resistance of mercury drops to zero when cooled to -269 degrees Celsius. With this discovery, the scientific world proved for the first time that materials can have superconducting properties. Researchers later discovered that other metals and alloys were also superconducting at extremely low temperatures.

When the calendars showed 1986, scientists discovered the copper oxide class, which showed the same decrease in resistance but at a higher temperature – about -196°C. These materials came to be known as “high temperature” superconductors, but they still needed to be cooled well below freezing. This discovery sparked the race to find superconductors that could operate at even warmer levels, including at room temperature.

Decades of research and multiple claims of superconductivity arose and were forgotten. And finally, last month, scientists from the Quantum Energy Research Center in Seoul, South Korea, published a preprint study claiming that a substance called “LK-99” exhibits superconducting properties even at temperatures as high as 127°C. Named after lead researchers Sukbae Lee and Ji-Hoon Kim (Lee/Kim-99), the material was literally phenomenal as it claimed superconductivity over a wide range of temperatures.

Pure LK-99, a purple crystalline compound produced from copper, lead, phosphorus and oxygen (Pb8.8Cu1.2P6O25), has been under investigation by scientists around the world for some time now. The results are once again disappointing.

Super insulator, not superconductor

On August 14, scientists from the Max Planck Institute for Solid-State Research in Stuttgart, Germany reported that the resistance of the claimed LK-99 is measured in millions of ohms, rather than falling to 0.02 to 0.002 ohm-cm. . What this means is this: Let alone being a superconductor, the material actually has a super-insulating structure.

However, this raised the question of how Lee and Kim demonstrated the superconducting properties of LK-99. They showed that the material exhibits the Meissner effect as it rises above a magnet – a hallmark of superconducting materials. There was also a notable drop towards near zero resistance.

But the half-lift shown in the video of the study caught the attention of other researchers. Noticing how one edge of the LK-99 particle sticks to the magnet, Derrick van Gennep, a former condensed matter researcher from Harvard University, confirmed that the effect demonstrated was due to ferromagnetism. Ferromagnetism is a property in which the material spontaneously generates a permanent magnetic moment in a magnetic field. However, this effect gradually disappears as the temperature increases.

The LK-99 sample was actually not pure

However, it turned out that Lee and Kim did not work with pure LK-99 because traces of sulfur were found in the samples used in the study. Prashant Jain, a chemist at the University of Illinois, noted that the chemical reaction Lee and Kim used to synthesize LK-99 created a copper-sulfur impurity.

The reaction that synthesizes LK-99 actually uses an unstable recipe. To obtain LK99, 17 parts of copper and 5 parts of sulfur are produced from copper doped lead phosphate crystal. These residues lead to numerous impurities, particularly the copper sulfide that the Korean team reported in their sample. We’ll talk a little bit about sulfur here.

They were quite precise about the temperature they were talking about when the resistance of the material behind the LK-99 was decreasing: 104.8 degrees Celsius. Those who are close to chemistry may have a light bulb in their minds because copper sulfide (Cu2S) undergoes a phase transition at 104ºC. Almost the same correlation with the LK-99’s phase transition couldn’t be ignored, of course, but it’s interesting that they overlooked it. So the team behind LK-99 may have thought that the material is superconducting because of the effect of this copper sulfide.

As a result, the scientific world seems to agree that LK-99 is definitely not a superconductor.