US researchers discover superconductor “better than graphene”

Stanene lattice

Stanene lattice

Researchers in the US believe they may have discovered a new ‘super-conductive’ material which could out-perform graphene.

Like graphene it is a material with a single layer of atoms, but unlike graphene it is constructed from a single layer of tin atoms.

The material has been called “stanene”.

It is the “first material to conduct electricity with 100% efficiency at the temperatures that computer chips operate”, according to a team of theoretical physicists led by researchers from the U.S. Department of Energy’s (DOE) SLAC National Accelerator Laboratory and Stanford University.

“Stanene could increase the speed and lower the power needs of future generations of computer chips, if our prediction is confirmed by experiments that are underway in several laboratories around the world,” said the team leader, Shoucheng Zhang, a physics professor at Stanford and the Stanford Institute for Materials and Energy Sciences (SIMES), a joint institute with SLAC.

According to Zhang, the first application could be in on-chip connections in a microprocessor.

“Eventually, we can imagine stanene being used for many more circuit structures, including replacing silicon in the hearts of transistors,” Zhang said.

The research team has been working for 10 years calculating and predicting the electronic properties of a special class of materials known as topological insulators, which conduct electricity only on their outside edges or surfaces and not through their interiors.

When topological insulators are just one atom thick, their edges conduct electricity with 100 percent efficiency. These unusual properties result from complex interactions between the electrons and nuclei of heavy atoms in the materials.

“The magic of topological insulators is that by their very nature, they force electrons to move in defined lanes without any speed limit, like the German autobahn,” Zhang said. “As long as they’re on the freeway – the edges or surfaces – the electrons will travel without resistance.”

Previous research looked at mercury telluride and several combinations of bismuth, antimony, selenium and tellurium, but none of those materials was found to be a perfect conductor of electricity at room temperature.

Earlier this year, visiting scientist Yong Xu, who is now at Tsinghua University in Beijing, collaborated with Zhang’s group to consider the properties of a single layer of pure tin.

“We knew we should be looking at elements in the lower-right portion of the periodic table,” Xu said. “All previous topological insulators have involved the heavy and electron-rich elements located there.”

Their calculations indicated that a single layer of tin would be a topological insulator at and above room temperature, and that adding fluorine atoms to the tin would extend its operating range to at least 100 degrees Celsius (212 degrees Fahrenheit).

The team’s work was published recently in Physical Review Letters (27 Sept 2013 (10.1103/PhysRevLett.111.136804)).

Additional contributors included researchers from Tsinghua University in Beijing and the Max Planck Institute for Chemical Physics of Solids in Dresden, Germany. The research was supported by the Mesodynamic Architectures program of the Defense Advanced Research Projects Agency.

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