In July 2023, two South Korean experimental physicists, Lee Sukbae and Kim Ji-Hoon published a pre-print in arXiv, claiming discovery of superconductivity in a sample, occurring at room temperature.  

The condensed matter physics community was put under spotlight in the wake of this paper, triggering a frenzy like none other in recent times.

The material dubbed, LK-99, after the initials of the South Korean physicists, promised nothing short of a revolution to the electronics industry.

But before I go further, let’s go through some superconductivity basics.  

What are superconductors?

Basically, superconductivity is a macroscopic quantum phenomenon. Our story begins with two ground-breaking experiments.

In 1911, the Dutch physicist, Heike Onnes observed that a mercury wire dipped in liquid helium, offered zero resistance to the passage of electricity, when the temperature of the mercury was lowered to-269^◦ C.

In 1937, Pyotr Kapitsa, John F. Allen and Don Misener discovered that at an even lower temperature close to -273^◦ C, liquid helium-4 transformed into a superfluid. A superfluid’s an exotic fluid exhibiting zero viscosity.

Both these exotic phenomena of superfluidity and superconductivity are closely linked, though they’re not the same.

However, this effect would go for years without a solid theory, until the physicists’ trio, John Bardeen, Leon Cooper and John Schrieffer, put together a ‘complete’ microscopic theory, known as the ‘BCS theory’. The theory makes a number of quantitative predictions about the behavior of superconductors. Most importantly, it shows how pairs of electrons would couple to form Cooper pairs, overcoming mutual repulsion below a set critical temperature. Bardeen, Cooper and Schrieffer would go on to win the 1972’s Nobel Prize in Physics for this work.

As much as superconductors revolutionized the electronics industry in the 20^th century, the temperatures at which this effect is commonly seen is in the same regime as outer space. It takes resources for laboratories to reach these temperatures. But imagine if nature showed us a material that can become a superconductor at room temperature …

The case for ‘room temperature’ superconductors

But you may be wondering what’s the big deal with room temperature superconductors anyway? For one, they’re promising an overnight revolution of sorts in the electronics industry. The approximately 7% loss of energy there is to pass currents through wires during transportation, can be brought down to near zero with room temperature superconductors. Another important use of these superconductors would be in the development of strong magnetic fields. Strong stable magnetic fields are used in MRI imaging and maglev trains.

Source: Ramon Salinero / Unsplash

This could make such technologies more accessible and cheaper to the public. Renewable energy generation from solar and wind power could see their efficiency rise with the help of room-temperature superconductors. The use of room-temperature superconductors could grow exponentially more after its discovery, even in applications we do not know yet. Think of the world today without any semiconductors, it would be tough to live without our LED lamps or solar panels. Similarly, room temperature superconductors could inexorably revolutionize our way of living for the better. I mean, who knows? Nobody knows! It’s yet to be invented.

Sukbae and Kim claimed that LK-99 displayed superconductivity when the temperature dropped below 127^◦ C. They claimed to have observed zero resistance currents.

And that was all it took for social media savvy tech entrepreneurs to embark on a hype train, and spread the word on room temperature superconductors potentially being real at last. Except it’s not technically room temperature – for 127^◦ C is way past the boiling point of water. But it’s much easier for laboratories to set up an experiment, investigate and replicate 127^◦ C.

The dream fever isn’t abating away, but the proof really is in the pudding.

There’s nothing to say room temperature superconductors can’t exist. In fact, scientists who worked in producing these results have also shared this opinion in their work.

Conventional superconductivity – with extreme cold critical temperatures – was challenged back in 1986, when certain cuprate compounds such as yttirium barium copper oxide (or YBCO) were discovered. They have a higher critical temperature of -183^◦ C, which is still very cold, but still warmer compared to helium-4. Such critical temperatures are outside the realm of the standard BCS theory, with the main mechanisms underpinning them being a topic of research.

The race for verification

After their paper was submitted in arXiv, Sukbae and Kim released a video of the levitating LK-99 sample on a magnet – a hallmark signature of the Meissner effect. The Meissner effect is a prediction of the standard BCS theory – when magnetic field lines are ousted from within the material itself.

They provided a detailed description of how LK-99 can be synthesised. This led materials labs from across the world to descend into a frenzy to try and replicate their results. 

Some of the earliest research were done at the National Physics Laboratory (NPL) in New Delhi and Beihang University in Beijing (BU).

A team from the Southeast University in Nanjing, observed a near-zero resistance in LK-99 at -163 ^◦ C. The team from Nanjing used an X-ray diffraction technique consistent with the work that the Korean scientists had published.

And then the theorists entered the fray. Sinead Griffin from the Lawrence Berkeley National Laboratory, US, performed calculations to suggest there really were telltale signs of room temperature super conductance in LK-99. Specifically, possible mechanisms for forming Cooper pairs were identified.

While these results were tantalising, they did not give conclusive evidence of superconductivity.

The Meissner effect – or what the South Koreans claimed was the Meissner effect- couldn’t be replicated in any other studies.

Griffin attained social media popularity after her tweets with over 14K followers on X.  However, truth be told – Griffith wasn’t explicitly backing anybody – but was merely giving the South Koreans’ work a fair shot.

The last twist in the saga came when she said, “My paper did *not* prove nor give evidence of superconductivity”.

Realization dawns

And suddenly, it wasn’t going in LK-99’s favour at all. It turned out the research team at Southeast University in Nanjing, had made incorrect measurements using faulty instrumentation, meaning they were unreliable.

Whereas, the studies from India’s National Physical Laboratory (NPL) and Beihang University didn’t find report any superconductivity effect. In fact, it just seemed like dull, grey metal.

But the final series of nails in the coffin were the conclusive results by Yuan Li at Peking Institute, and Yi Jiang at the Donostia International Physics Centre, Spain. They proved beyond doubt that LK-99, as synthesised by the South Korean team, was a ferromagnet. Yuan Li also explained the levitating video of LK-99 pellets over a magnet was a result of ferromagnetism. He also showed the absence of superconducting current at low temperatures.

A ferrofluid exhibiting ferromagnetic properties; Source: Etienne Desclides / Unsplash

Science is often rife with controversies and debatable results. Many physicists have published unconfirmed, and published plagiarized work. Some notable examples include the alleged groundbreaking work of Jan Schön, who claimed discovery of organic transistors. Only to be charged with fraud after he made up his results, thus bringing him disrepute that brought an end to his scientific career pretty early on.

Then there was the work by Anshu Pandey and Dev Thapa on similar claims of room temperature superconductors that weren’t replicated.

Although it’s unfortunate that this saga ended so disappointingly with LK-99, I am not, in any manner suggestive of the fact that room-temperature superconductivity cannot exist.

Scientists who worked in producing these results have also shared this opinion in their work. Many scientists have however also shared the need to understand the results and related nitty gritty, before jumping the gun.

However, the collaboration amongst scientists at universities across the world, was focused on uncovering LK-99’s true properties.

It wasn’t just mere claims, backed by data, but also the peer-review process that helped redefine public discourse, and set the facts straight. And that had made all the difference.