Lithium Atoms Turn Graphene into a Superconductor

Physicists in Canada and Germany have proved that graphene turns into a superconductor when ‘decorated’ with lithium atoms, which could lead to a new generation of superconducting nanoscale devices, according to Nanotechweb.org.

In 2005, physicists demonstrated that when chemically treated, graphite could exhibit superconducting properties.

“Theorists identified the underlying mechanism for that superconductivity as electron–phonon coupling. Phonons are vibrations in a material’s crystal lattice that bind electrons together into “Cooper pairs” that can travel through the lattice without resistance – one of the hallmarks of superconductivity. It was then realized that such electron–phonon coupling might occur not just in bulk graphite compounds but also by depositing atoms of a suitable element on to single layers of graphene,” according to researchers.

Then, in 2012, Gianni Profeta from the University of L’Aquila in Italy, along with his colleagues, used computer modeling to predict that lithium could be a good candidate for coupling.

“This came as a surprise, given that bulk LiC6 had not been shown to superconduct, but the researchers nevertheless found that the monolayer structure should promote superconductivity in two ways. The additional lattice vibrations generated by the lithium atoms should yield a high density of phonons, they said, while lithium’s donation of electrons to the graphene should strengthen overall electron–phonon coupling,” according to Nanotechweb.org.

This knowledge assisted Andrea Damascelli from the University of British Colombia in Vancouver and a team in Europe to fully transform Graphene into a superconductor. The physicists achieved this by growing layers of graphene on silicon-carbide substrates and then depositing lithium atoms onto the graphene in a process known as “decorating.”

“The team then studied the properties of the samples using angle-resolved photoemission spectroscopy, which exploits the photoelectric effect to measure the momentum and kinetic energy of electrons in a solid. The researchers found that the electrons were being slowed down as they travelled through the lattice, an effect that they attributed to enhanced electron–phonon coupling. Crucially, they also showed that this greater coupling leads to superconductivity by identifying an energy gap between the material’s conducting and non-conducting electrons – which is the energy needed to break Cooper pairs. At 0.9 meV, the measured value of this gap implies a transition temperature of about 5.9 K – as compared with Profeta and colleagues’ prediction of up to about 8 K,” according to Nanotechweb.org.

The next step for the team is to demonstrate superconductivity in a single layer of graphene and to incorporate this single substrate into electronic devices.

Original Source http://ift.tt/1Fg3XTw

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