How scientists found that LK-99 is probably not a superconductor?

Subject: Science and technology

Section :Msc

Context:

A substantial amount of electricity generated is lost while being transmitted between power plants and our factories and households as heat.
Tiny wires inside computers and cellphones dissipate heat, draining the batteries in the process. So it is natural that scientists are looking for materials that can conduct electricity without resistance.

An elusive material:

Many metals become superconducting – i.e. allow current to flow with zero resistance – if cooled to below -250º C.
Superconductors aren’t just materials with zero resistance, they have a new quantum state in which the electrons in the material work together.
Several properties of superconductors brought new technologies including advancedmedical imaging, ‘maglev’ trains, and quantum computers.
However, superconductivity also remained an extremely-low temperature-phenomenon for a long time.
In the mid-1980s scientists discovered copper-oxide superconductors, whose transition temperature was higher than -200º C.
But to this day, scientists haven’t discovered a material that acts as a superconductor at ambient conditions (room temperature).
One of the highest transition temperatures has been found in a sulphide compound, but it needs to be placed under extreme pressures – like that found at the centre of the earth.

Surprise and skepticism:

In July 2023, a group of scientists in South Korea claimed that a lead apatite material was an ambient condition superconductor.
- Apatites are materials that have a regular arrangement of tetrahedrally shaped phosphate ions (i.e. one phosphorus atom and four oxygen atoms).
- When lead ions sit in between these phosphate motifs, it is lead apatite.
The novelty of the South Korean group’s work was to replace 10% of the lead ions in lead apatite with copper, to produce the room-temperature superconductor named LK-99.

What made the South Korean team think of LK-99 a superconductor?

While measuring a material’s electric resistance, the resistance drops below a certain temperature.
- The resistive state was restored if a sufficiently large amount of current was passed through the sample.
The low resistance state vanished when a sufficiently strong magnetic field was applied.
LK-99 was partially levitating over a magnet– a famous test for superconductivity.

Why are scientists denying superconductivity of LK-99?

The group missed several crucial tests, including some to confirm the quantum nature of the microscopic state of the system.
The Indian group, from the CSIR-National Physical Laboratory, New Delhi, was one of the first to report that it didn’t find any signs of superconductivity in LK-99.
Scientists across the world noticed:
- No drop of resistance
- LK-99 shows properties of the insulator and it shows ferromagnetism.
Superconductors cannot have this property.

Why did LK-99 show some properties of ambient conditions superconductors?

The copper sulphide (a by-product in LK-99), caused the drop in resistance.
Researchers pointed out that the levitation was also due to the impurities present in LK-99, as some impurities are diamagnetic.
- Diamagnetic materials can also partially levitate above magnets as a result.
The current evidence suggests that LK-99 is not a superconductor.
Scientists found that if copper atoms replaced a certain set of lead atoms in LK-99, the material would act like a flat-band system.
- Electrons in flat-bands can interact strongly with each other and are predicted to form superconducting phases, but only at very low temperatures.