Pressure dependence of the critical superconducting temperature of a metal created by the team from carbon disulphide molecule (top left) was measured by electrical contacts (inset in the middle) and electromagnetic coils (inset at the bottom) (CREDIT: WSU)

Superconductor created from non-metallic solvent

A non-metallic solvent used as an insecticide has been turned into a superconductor by researchers in the US.

A team lead by Choong-Shik Yoo, professor of chemistry and Institute for Shock Physics at Washington State University, has turned carbon disulphide into a material capable of transmitting electrical current with none of the resistance seen in conventional conductors.

The discovery is surprising as typically non-metallic molecules are too far apart from each other – three times farther apart than metal molecules – for electrical energy to move across them.

The team, including researchers at the Carnegie Institution of Washington, compressed the compound in a diamond anvil cell to 50,000 atmospheres, a pressure equivalent to that found 600 miles into the Earth, as well as chilling the compound to 6.5 degrees Kelvin, or nearly -266°C.

The pressure and temperature caused the compound to start acting like a metal, taking on properties like magnetism, a high energy density, and superhardness as its molecules reassembled in three-dimensional structures like those found in diamonds.

In a study that appears in yesterday’s issue of the Proceedings of the National Academy of Sciences, Yoo and doctoral student Ranga Dias explain how the carbon disulfide molecules rearrange into a lattice structure in which the natural vibrations of the molecules can help electrons move so well the material becomes a resistance-free superconductor.

"It is an important discovery that will attract a lot of attention from many scientific communities; physics, chemistry, and materials science," says Yoo. "What makes this discovery special is that it seems counter to the understanding of how superconductivity normally works."

Usually superconductivity is present in highly ordered molecular structures, but in carbon disulfide superconductivity arises from a highly disordered state, which is rare.

Even more surprising, this disordered structure is preceded by a magnetically ordered state, which undergoes a structural change into the disorganized configuration when superconducting starts.

"These results show the interplay between superconductivity, magnetism and structural disorder," says Carnegie Institution researcher Viktor Struzhkin. "We are already at work searching for other highly conducting states in similar molecular systems in close collaboration with Professor Choong-Shik Yoo's team."

The field of superconductivity has a wide variety of potentially revolutionary applications, including powerful electromagnets, vehicle propulsion, power storage and vastly more efficient power transmission.

Yoo's research provides new insight into how superconductivity works in unconventional materials, an area that has intrigued scientists for several decades, he says.

These unconventional materials are typically made of atoms with lower atomic weights that let them vibrate at higher frequencies, increasing their potential as superconductors at higher temperatures.

Yoo acknowledges that electronic materials are not about to be cooled to near absolute zero or subjected to extreme pressures, but he says this work could point the way to creating similar properties under more ordinary conditions.

"This research will provide the vehicle for people to be clever in developing superconductors by understanding the fundamentals that guide them," says Yoo.

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