A recent discovery in a study of room-temperature superconductivity, if borne out, could make the dream of super-efficient long-distance electricity transmission and levitating trains a little closer to reality.
Whereas physicists understand how standard superconductors can operate at nearly 275 degrees Celsius below water's freezing point, the mechanism behind high-temperature superconductors, which function at up to 140 degrees warmer than absolute zero, remains mysterious. Without knowing exactly how these warmer substances would manage to conduct electricity with zero resistance, researchers still don't know whether it's possible for anything to be superconductive at comparatively hot room-temperature conditions—which is what a new study claims.
According to a paper in Advanced Materials, cheap and easily obtainable graphite powder exhibits signs of superconductivity. And it doesn't need to be chilled with an expensive cryostat system—all it takes to make the powder superconductive is a simple water bath.
Pablo Esquinazi and other physicists from the University of Leipzig first discussed graphite as a potential superconductor in a 2012 paper published on arXiv, an electronic archive of preprint scientific papers. (The researchers have also made their new paper available there.) Certain parts of the material showed signs of the Josephson effect, when electrons tunnel between a barrier separating two superconductors. The effect indicated that the graphite samples contained superconducting areas.
"Due to this and the work we did the last three years, we were sure that superconducting patches could be possible," Esquinazi says. To test this notion the researchers treated graphite powder with water: They stirred it into the liquid for 23 hours, filtered it out and dried it at 100 degrees Celsius. Then they tested how the water-treated powder responded to a changing magnetic field.
Graphite, along with other materials, has held out the promise of room-temperature superconductivity before. For years there have been reports of weak, indirect superconducting signals coming from graphite treated with elements such as sulfur and oxygen. But nobody, not even these researchers, has been able to produce a definite room-temperature superconductor, a material that repeatedly meets the textbook definition of superconductivity—the conduction of electricity with zero resistance.
There are, however, other characteristics that mark a superconductor: A material typically becomes superconductive when it passes a temperature threshold and undergoes a distinct phase transition. The Josephson effect is another sign of superconductivity, and there is also the Meissner effect, also known as diamagnetism: When exposed to an external magnetic field, a superconductor pushes that field away so it doesn't penetrate the material. The magnetic field inside the superconductor will be less than the field outside. This effect makes it possible for superconductors to levitate, and it also creates detectable changes in the external magnetic field, providing a measurable sign of superconductivity.
The physicists tested their treated graphite powder for diamagnetism by measuring its magnetization as it was exposed to a changing magnetic field. And it responded as if a fraction of the sample was indeed superconducting—but only a tiny fraction of 0.01 percent.