Adding calcium atoms (orange) between graphene planes (blue) creates superconducting material CaC6

Potential key to superconducting graphene discovered

A potential method for making graphene superconducting could help engineer materials for super-efficient nanoelectronics.

Superconductivity is a state in which materials carry electricity with 100 per cent efficiency and scientists at the US Department of Energy's SLAC National Accelerator Laboratory and Stanford University believe they may have found the key to inducing this state in the wonder material, which consists of a single layer of carbon atoms.

The researchers used a beam of intense ultraviolet light to look deep into the electronic structure of a material made of alternating layers of graphene and calcium, a material that is already known to be superconducting.

But the new study offers the first compelling evidence that the graphene layers are instrumental in this process, a discovery that could transform the engineering of materials for nanoscale electronic devices.

"Our work points to a pathway to make graphene superconducting – something the scientific community has dreamed about for a long time, but failed to achieve," said Stanford graduate student Shuolong Yang, who led the research at SLAC's Stanford Synchrotron Radiation Lightsource (SSRL).

In an article published in journal Nature Communications yesterday, the researchers described how electrons scatter back and forth between graphene and calcium, interact with natural vibrations in the material's atomic structure and pair up to conduct electricity without resistance.

Samples calcium intercalated graphite or CaC6, made by chemically interweaving graphite with crystals of pure calcium, were made at University College London and brought to SSRL for analysis.

"These are extremely difficult experiments," said Patrick Kirchmann, a staff scientist at SLAC and Stanford.

But the purity of the sample combined with the high quality of the ultraviolet light beam allowed them to see deep into the material and distinguish what the electrons in each layer were doing, he said, revealing details of their behaviour that had not been seen before.

"With this technique, we can show for the first time how the electrons living on the graphene planes actually superconduct," said Stanford graduate student Jonathan Sobota, who carried out the experiments with Yang. "The calcium layer also makes crucial contributions. Finally we think we understand the superconducting mechanism in this material."

Although applications of superconducting graphene are speculative and far in the future, the scientists said, they could include ultra-high frequency analog transistors, nanoscale sensors and electromechanical devices and quantum computing devices.

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