Last week, there was a lot of talk about a superconductor that works at room temperature. Here’s what we know about it.

Since they were first discovered in 1911, superconductors, which are materials that conduct electricity perfectly, have fascinated physicists. They’re used in various technologies like particle accelerators, MRI machines, and maglev trains. However, their practical use is limited because they only work at very low temperatures.

On July 22, scientists from South Korea reported a breakthrough. They claimed to have created a material called LK-99 that becomes nearly resistant to electrical current at a temperature of 30 degrees Celsius (86 degrees Fahrenheit). This discovery has triggered a worldwide effort to reproduce the material and verify its properties. However, as of August 4, no one has been able to confirm the results.

Here’s everything you need to know about superconductors. 

What is superconductivity?

Superconductivity is a property found in certain materials where they can conduct electricity with zero resistance when cooled to very low temperatures. In normal materials, electrical current encounters resistance as electrons collide with ions. However, in superconductors, as the temperature decreases, the vibrations of ions decrease, causing collisions to decrease and resistivity to drop sharply.

This allows electrical current to flow freely without losing energy. The first superconductor was discovered in 1911 by Dutch physicist Heike Kamerlingh Onnes, who found that a supercooled mercury wire no longer resisted electricity at extremely low temperatures, earning him a Nobel Prize in Physics.

How do superconductors work?

Despite Onnes’s groundbreaking discovery of superconductivity in 1911, it took several decades to understand why it occurred. The breakthrough came in 1957 with the development of the BCS theory, named after its creators John Bardeen, Leon Cooper, and John Robert Schrieffer.

This theory proposed that superconductivity arises from electron interactions that create ripples in the material. At very low temperatures, these ripples cause atomic nuclei to attract each other, leading to a slight charge offset that draws a second electron toward the first. This attraction results in electrons forming pairs called “Cooper pairs,” which behave differently from individual electrons and contribute to superconductivity.

Cooper pairs, unlike solitary electrons, obey unique quantum mechanical principles. Instead of organizing into energy shells, they behave akin to particles of light, capable of occupying the same space simultaneously in infinite numbers. When a sufficient number of Cooper pairs forms within a material, they transform into a superfluid state, allowing them to flow without any dissipation of energy.

Once set in motion, a superfluid can theoretically continue swirling indefinitely, persisting until the end of the universe.

However, the story of superconductivity had more surprises in store for physicists. In 1986, Alex Müller and Georg Bednorz of IBM made a groundbreaking discovery. They found that materials known as cuprates, composed of layers of copper and oxygen sandwiched between other elements, could exhibit superconductivity at temperatures as high as minus 211 degrees Fahrenheit (minus 135 degrees Celsius).

The exact reason behind this phenomenon is not completely understood, but the leading theory comes from the American physicist Phillip Anderson. He proposed that electrons opt to exchange positions with each other through a quantum mechanical process known as superexchange.

Electrons continually attempt to exchange positions because, like all particles and many natural phenomena, they strive to occupy the lowest energy state possible. According to Heisenberg’s uncertainty principle, which states that only a particle’s position or momentum can be precisely known at any given time, electrons move to make their positions uncertain and their momentum well-defined.

This constant switching leads to the electrons’ energies being more precisely defined, allowing them to settle into the lowest possible energy state. And the perfect arrangement for this switching to occur? It turns out to be a sea of evenly-spaced Cooper pairs.

Recent experiments indicate that Anderson’s theory may hold true, at least for the materials under examination. However, superexchange could potentially be just one form of electron interaction among several. It remains uncertain how effectively these hypothetical electron interactions could function at higher temperatures and which engineered materials could facilitate these interactions.

Superconductors are recognizable by a distinct characteristic: levitation. When materials become superconductors, the electrons flow without resistance, creating a magnetic field. This field can then repel an external magnet with an equal and opposing force. When a superconductor is positioned above a magnet, it remains perfectly suspended in the air due to this phenomenon, known as the Meissner effect.

Are room temperature superconductors possible?

Room temperature superconductors do not defy any established physics theories, but currently, no theories predict their existence either. The challenge lies in the realm of engineering, presenting a formidable puzzle involving a vast array of atoms and chemical properties spanning numerous material combinations to explore.

Scientists have explored various materials in their quest for room temperature superconductors. Among them is graphene, which exhibits low-temperature superconductivity that can be toggled on or off based on the twists and turns of its one-atom-thick layers. Another potential contender is scandium, a silvery metal. Recent studies indicate that scandium can achieve superconductivity at higher (albeit still very cold) temperatures.

A controversial claim surfaced in 2020 when researchers reported observing a mixture of carbon, sulfur, and hydrogen superconducting at 57°F (14°C) under high pressures beneath two diamonds. A subsequent experiment in 2021 purported even higher temperatures, up to 70°F (21°C), for a larger sample of the material. However, after scrutiny by other scientists, the 2020 paper was retracted due to accusations of data manipulation and plagiarism against the research team.

LK-99, a novel material composed of mixed powders containing lead, oxygen, sulfur, and phosphorus doped with copper, has emerged onto the scene with the remarkable claim of near-zero resistivity at 86°F (30°C). Its relative ease of manufacture and testing adds to its allure. However, of the 11 attempts to replicate the results, only three out of seven observed properties akin to those asserted for LK-99, with the remaining four noting neither magnetism nor superconductivity.