Room-temperature superconductors: why the claims keep failing

What a superconductor is

Below a certain temperature some materials lose all electrical resistance and push magnetic fields out of themselves. Both effects appear together and both are needed to prove the state is real. Zero resistance alone can be faked by a bad contact. Magnetic expulsion alone can be mimicked by ordinary magnetism.

The catch is temperature. Most known superconductors need cooling to well below the coldest natural place on Earth. The record holders that work near room temperature so far need pressures found only deep inside planets.

The 2023 episode

In July 2023 a preprint claimed a copper-doped lead compound, nicknamed LK-99, superconducted at room temperature and ordinary pressure. A short video showed a chip partly levitating over a magnet. Within days, labs worldwide tried to make it.

Within weeks the picture was clear. The material was an insulator. The partial levitation was ordinary diamagnetism plus a lump of shape. The sharp drop in resistance that had looked like a transition was traced to an impurity, copper sulphide, which changes its behaviour near 104 degrees Celsius.

Why this keeps happening

Superconductivity has three failure modes that look like success:

• Impurity transitions. A tiny contaminant can produce a step in resistance at a fixed temperature.
• Contact effects. Four-probe measurements are supposed to remove contact resistance, but poor contacts on a small sample still create artefacts.
• Weak magnetic signals. Diamagnetism is common. Only a full expulsion of field, measured carefully, counts.

A prior high-profile claim, for a hydrogen-rich compound under pressure, was retracted in 2022 after questions about how the data had been processed. A second claim from the same group was retracted in 2023.

What real progress looks like

Real advances in this field arrive quietly. Computer prediction of hydrogen-rich compounds, followed by synthesis under pressure, has pushed confirmed transition temperatures up steadily. The measurement standards have tightened as a result of the failures: raw data, independent samples and a magnetic test are now expected before anyone gets excited.

How to read the next claim

Ask three questions. Has anyone outside the original group made the material? Do resistance and magnetism both show the transition at the same temperature? Is the raw data available? If the answers are no, wait.