The LK-99 Saga: Why Room-Temp Superconductivity Failed

In July 2023, the scientific community and social media exploded with news of a potential revolution. A team of researchers in South Korea claimed they had created the “holy grail” of physics: a room-temperature, ambient-pressure superconductor. They called it LK-99. While the excitement was palpable, the claim ultimately crumbled under scrutiny. Here is a detailed look at what happened, why the material failed to meet the criteria, and what this means for science moving forward.

The Promise of a Physics Revolution

Superconductivity is a state where a material conducts electricity with zero resistance. It means no energy is lost as heat. Currently, we can only achieve this at extremely low temperatures (near absolute zero) or under crushing pressure.

On July 22, 2023, Sukbae Lee and Ji-Hoon Kim from the Quantum Energy Research Centre in Seoul uploaded two preprints to the server arXiv. They claimed their material, a modified lead-apatite structure branded as LK-99, exhibited superconductivity at temperatures up to 127°C (400 Kelvin).

This claim was massive. If true, it would transform everything from power grids and MRI machines to magnetic levitation trains and quantum computers. The authors provided two main pieces of evidence:

1. Zero Resistance: A graph showing electrical resistance dropping to near zero.
2. Levitation: A video showing a small chunk of the material floating over a magnet.

The Replication Race

Because the recipe for LK-99 was relatively simple, labs around the world immediately tried to cook it themselves. The material is made by mixing powders of lanarkite and copper phosphide, then baking them in a vacuum.

The initial results were confusing.

• Huazhong University of Science and Technology (China): A team here managed to replicate the crystal and released a video that appeared to show levitation. This fueled the hype.
• Southeast University (China): Researchers here measured zero resistance, but only at -163°C (110 Kelvin), which contradicted the room-temperature claim.
• National Physical Laboratory of India: This team synthesized the material but found it was highly resistive. In fact, they found it acted more like an insulator than a metal.

As weeks passed, the consensus shifted from excitement to skepticism. The data simply wasn’t consistent.

The Culprit: Copper Sulfide Impurities

The primary reason the original South Korean team was fooled came down to a specific impurity. When synthesizing LK-99, the process creates a byproduct called copper(I) sulfide (chemical formula Cu2S).

This impurity is the key to the misunderstanding. Prashant Jain, a chemist at the University of Illinois Urbana-Champaign, pointed out a critical flaw in the original data. Cu2S undergoes a “phase transition” at approximately 104°C (377 Kelvin).

During this phase transition, the crystal structure of the copper sulfide changes. This change causes a sharp drop in electrical resistance. The original researchers saw this drop and interpreted it as the onset of superconductivity. In reality, they were measuring the behavior of the dirt (impurities) inside their sample, not the LK-99 material itself.

Debunking the Levitation

The video of the floating rock was the most viral aspect of the saga. True superconductors exhibit the Meissner effect. This is where the material expels magnetic fields, causing it to lock in place or float seamlessly above a magnet.

However, the LK-99 sample in the video was only “half-levitating.” One edge remained touching the magnet while the other tilted up.

Researchers at Peking University and the Center for High Pressure Science and Technology Advanced Research offered a different explanation: Ferromagnetism.

They found that the original samples likely contained iron or other magnetic impurities. The “levitation” was actually just the material sticking to the magnet at an angle due to magnetic attraction, similar to how a paperclip might stand up on a magnet without fully floating. It was not the Meissner effect.

The Final Verdict: Max Planck Institute

The saga effectively ended in mid-August 2023. A team at the Max Planck Institute for Solid State Research in Stuttgart, Germany, successfully synthesized pure single crystals of LK-99.

By using a technique called floating zone crystal growth, they eliminated the copper sulfide impurities that had plagued other samples. Their results were definitive:

1. Purple Crystals: The pure LK-99 crystals were transparent and purple.
2. Insulator: The material was not a superconductor. It was not even a metal. It was an insulator with a resistance in the millions of ohms.

The Max Planck team concluded that LK-99 is a trivial insulator. The superconductivity observed by the original team was entirely due to the copper sulfide impurities.

What This Means for Future Material Science

While the failure of LK-99 was a disappointment, the event was a fascinating stress test for modern science.

The Speed of Open Science

The saga highlighted the power of preprint servers like arXiv. In the past, this debunking process might have taken two years of peer review behind closed doors. With LK-99, the global scientific community crowdsourced the replication and debunked the claim in less than four weeks.

The Difficulty of Synthesis

This event reminded the world that material science is messy. Making a pure sample is difficult. The difference between a revolution and a mistake often comes down to a few micrograms of dirt or a misinterpreted phase transition.

Continued Hope

Despite this failure, the search continues. High-temperature superconductivity remains physically possible. Researchers are using AI and machine learning to predict new crystal structures that might finally achieve the goal. LK-99 was a false start, but the race is far from over.

Frequently Asked Questions

Did the original researchers admit they were wrong? As of late 2023, the original team at the Quantum Energy Research Centre stood by their claims, arguing that other labs did not prepare the samples correctly. However, the global consensus from major institutions (Nature, Max Planck) is that the claim is false.

Is LK-99 completely useless? Likely yes, in terms of electronics. Since pure LK-99 is an insulator, it cannot conduct electricity effectively. It might have niche interest for crystallographers, but it has no industrial application as a conductor.

Why did people believe it at first? The synthesis method was detailed and relatively easy to attempt. Unlike other claims that require rare isotopes or billion-dollar equipment, LK-99 could be made in a standard university furnace. This accessibility made people hope it was the “everyman’s” superconductor.

What is the current record for high-temperature superconductivity? We have achieved room-temperature superconductivity, but only under immense pressure (millions of atmospheres). For ambient pressure (normal air pressure), the record high temperatures are still well below freezing, generally requiring liquid nitrogen for cooling.