Claimed Room-temperature Superconductor Falters Under Scrutiny

Two papers published July 22, 2023, detail research by Sukbae Lee and Jihoon Kim of the Quantum Energy Research Center, South Korea, that has shaken the world of physics and beyond.

 

Rendering of a levitating superconductor. Image used courtesy of Adobe Stock (licensed)

 

The two studies announced the synthesis of a room-temperature superconductor, dubbed LK-99. The moniker refers to the initials of the two primary researchers, Lee and Kim, and 1999, the year they began studying the material.

 

The Significance of a Room-temperature Superconductor

LK-99 is a modified-lead apatite crystal with the chemical composition Pb_10-xCu_x(PO₄)₆O, where 0.9 < x < 1.1 reportedly has a superconducting critical temperature (Tc) above 126.85°C (400°K/260.33°F). On its own, lead apatite is a non-conducting mineral. According to the papers, the researchers turned the mineral into a superconductor by doping it with copper and phosphorous. If substantiated, this would be the world’s first room-temperature, ambient-pressure superconductor.

A second and equally important claim is that the material can be easily and inexpensively synthesized. The process to create LK-99 uses common elements and requires just three mixing and heating steps under vacuum conditions. At the time of this writing, at least a dozen groups are working to duplicate the synthesis effort, with about an equal number thus far reporting failure or partial failure vs. partial success. To date, no one has claimed full success in creating the material and verifying superconducting properties.

 

Process detail covered in section II of the original paper. Image used courtesy of arXiv

 

The claim, if proven, would likely be significant enough to warrant a Nobel Prize. However, the scientific community has not received the so-called breakthrough without controversy. As reported by Science staff writer Adrian Cho, some of the data looks less than credible, and the practices detailed in the papers do not engender confidence in the results. The first July 22 paper was published by a third researcher, Young-Wan Kwon, listing himself as a co-author. Later that day, Kim submitted the second paper. A follow-up report from Science suggests that this odd posting may reflect infighting among the team members, giving more reason for skepticism.

 

A Quick Refresher on Superconductivity

In all conventional metallic electrical conductors, the resistance gradually drops along with temperature until reaching a minimum level of resistance at absolute zero. A superconductor has a critical threshold temperature (Tc), typically a few degrees above absolute zero. Above Tc, resistance decreases along a curve like a conventional material. At Tc, however, the resistance suddenly drops to zero, allowing current to flow with no resistance and no heat loss.

 

As a superconductor temperature drops past its Tc, resistance jumps to zero rather than continuing on a gradual decreasing curve as does a non-superconductor. Image used courtesy of Physics Feed

 

In addition to the resistance-free current flow, superconductors exhibit the Meissner effect—the expulsion of magnetic fields from the material. This means a superconducting material will repel a nearby magnet, and it's one of the simplest tests of a superconductor. If you cool a material below its Tc and place a permanent magnet on top of the material in a superconducting state, the magnet will levitate due to the Meissner effect.

 

Below Tc, superconductors expel magnetic fields, meaning that a magnetic object will be repelled. Image used courtesy of Physics Feed

 

Current Flow With Zero Resistance

A superconductor exhibits zero DC resistance, meaning a current injected into a superconducting coil of wires can theoretically maintain flow indefinitely. For nearly 28 years, researchers at the Royal Observatory of Belgium have been running an experiment demonstrating the effect. The team injected current into the superconducting coils of their gravimeter in September 1995, levitating a 4-gram niobium sphere, which has not degraded since that time. The group achieves this feat by cooling the gravimeter with liquid helium to 4 degrees above absolute zero.

 

Liquid helium-cooled superconductor experiment at the Royal Observatory of Belgium going on 28 years. Image used courtesy of the Royal Observatory of Belgium

 

The difference between near absolute zero for a superconductor and zero for an ordinary metallic conductor may not seem significant, but temperatures of a few degrees above zero are attainable while absolute zero is not. Each degree higher than absolute zero means a lower cost to reach and sustain the superconducting state. 

Superconductors with a Tc above 77°K, the boiling point of liquid nitrogen, are referred to as high-temperature superconductors, or HTC. Because HTC can use liquid nitrogen, which is significantly more practical than liquid helium, much research has gone into the HTC field. However, a practical room-temperature superconductor would largely render that work obsolete, delivering resistance-free current flow and the Meissner effect without an expensive cooling system.

 

A Superconducting Society

The promise of room-temperature superconductors extends beyond the confines of a laboratory. Imagine a warehouse where the floor under the aisles is wired with a superconductor. In that scenario, hand carts equipped with magnets on the underside would literally levitate, allowing for near-zero effort movement. A highway equipped with superconductors could carry levitating cars. A superconducting power grid could carry significantly more power without current loss due to resistance and heat.

Almost every aspect of modern technology—virtually anything that utilizes electromagnetism—stands to dramatically improve in efficiency in a world with practical room-temperature superconductors.

 

The Scientific Community Awaits Confirmation or Dismissal

If the LK-99 is verified, the race will begin to monetize the material, and our world will never be the same. But the industry has good reason for caution. Back in 1989, two physicists, Fleischmann and Pons, set the scientific community ablaze with the announcement of a “successful” cold-fusion experiment. It didn’t take long for results to be completely refuted, but the stigma of jumping on the bandwagon of research yet to be peer reviewed still shadows the scientific community today.