This image shows the smallest superconductor, which is only .87 nanometer wide. (Saw-Wai Hla and Kendal Clark/Ohio University)
Scientists have discovered the world’s smallest superconductor - a sheet of four pairs of molecules less than one nanometer wide. The Ohio University-led study provides the first evidence that nanoscale molecular superconducting wires can be fabricated, which could be used for nanoscale electronic devices and energy applications.

“Researchers have said that it’s almost impossible to make nanoscale interconnects using metallic conductors because the resistance increases as the size of wire becomes smaller. The nanowires become so hot that they can melt and destruct. That issue, Joule heating, has been a major barrier for making nanoscale devices a reality,” said Saw-Wai Hla, associate professor of Physics and Astronomy and leader of the research team.

Superconducting materials have an electrical resistance of zero and can therefore carry large electrical currents without power dissipation or heat generation. Until recently, superconductivity was considered a macroscopic phenomenon. The current finding suggests that it exists at the molecular scale, which opens up a novel route for studying this phenomenon, according to Hla.

In the study, which was funded by the DOE, Hla’s team examined synthesized molecules of a type of organic salt - (BETS)2-GaCl4 - placed on a surface of silver. Using scanning tunneling spectroscopy, the scientists observed superconductivity in molecular chains of various lengths. For chains below 50 nanometers in length, superconductivity decreased as the chains became shorter. However, the researchers were still able to observe the phenomenon in chains as small as four pairs of molecules, or 3.5 nanometers in length.

To observe superconductivity at this scale, the scientists needed to cool the molecules to a temperature of 10 Kelvin. Warmer temperatures reduced the activity. In future studies, scientists can test different types of materials that might be able to form nanoscale superconducting wires at higher temperatures.

“But we’ve opened up a new way to understand this phenomenon, which could lead to new materials that could be engineered to work at higher temperatures,” Hla said.

(Ohio University)