Superconductors are extraordinary materials in which electricity flows without resistance, potentially enabling advances such as ultra-fast magnetically levitating trains. Now scientists find that even a fairly common liquid solvent can transform into a superconductor with the help of high pressure. The findings appearing online this week in the Proceedings of the National Academy of Sciences could help yield insights on how superconductors in general work.
Many substances become superconducting under extreme cold. Increasingly, researchers find that subjecting materials to high pressures can also help develop new superconductors. Until now, all these high-pressure materials were metallic or metal oxides, wherein molecules are close enough together for electrons to freely move across them. In comparison, nonmetallic molecules are roughly three times farther apart than metal ones in materials.
Chemist Choong-Shik Yoo at Washington State University in Pullman and his colleagues investigated carbon disulfide, a common industrial solvent that is nonmetallic. Under extreme cold and pressure, they noted the solvent began acting like a metal, taking on metallic properties such as magnetism and remarkable electrical conductivity.
In experiments, the researchers super-cooled carbon disulfide to 6.2 Kelvin (minus 267 degrees C, minus 448 degrees F), and under extreme pressures ranging from 50 billion to 172 billion pascals generated within a diamond anvil, the solvent became superconducting. (In comparison, the crushing pressure at the bottom of the Mariana Trench, the deepest point of the sea, is only about 110 million pascals.)
X-ray scattering analysis revealed the solvent’s molecules reassembled its three-dimensional structure under extreme cold and pressure from a tetrahedral configuration to an octahedral one. This shift allowed the natural vibrations of the molecules helped electrons move well enough for superconductivity to result.
Although the extreme cold and pressure needed to make carbon disulfide superconducting preclude it from any practical applications, “this work could point the way to creating similar properties under more normal ordinary conditions, much as science paved the way to make synthetic diamonds at lower pressures and temperatures,” Yoo says. “This research can provide a vehicle for people to be clever in developing superconductors by understanding the fundamentals that guide them.”