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Spectroscopic platform to study graphene

In the presence of a magnetic field, electrons can occupy only certain energy levels. Electrons can stay only in the bright stripes (technically known as Landau levels).

A spectroscopic platform has been developed to explain the electronic structure of graphene by physicists at the Korean Institute for Basic Science’s (IBS’) Centre for Theoretical Physics of Complex Systems (PCS), in collaboration with the Korean Research Institute for Standards and Science (KRISS).

In order to study the electronic properties of both single and double layer graphene, the team constructed a nanodevice with graphene sandwiched between two layers of an insulating material known as hexagonal boron nitride. On top of this device they placed graphite as electrode. The bottom layer consisted of one layer of silicon and one of silica.

By tuning the voltages applied via the graphite and the silicon, the scientists measured the changes in the conductance of graphene.

"We used an intuitive model to reproduce the experimental measurement and we gave a theoretical explanation to why these energy configurations form with single and double layer graphene," explained professor Myoung Nojoon.

Through modulating the applied voltages, the scientists could deduce the electronic structure of graphene by following the Fermi level. The electrons of graphene have a particular energy structure, represented by the Dirac cone.

In particular, they noticed that when the voltage applied to graphite is around 350mV, there is a dip in the conductance measurement, by which the Fermi level matches with the Dirac point.

The electrical properties change again when a magnetic field is applied to the single layer graphene. In this case, the data obtained by the scientists of KRISS was reproduced by IBS physicists, which showed more than 40 Landau levels. Each level was said to be clearly distinguishable because of the low background noise.

The scientists could also match the theoretical and experimental data relative to the electronic properties of bilayer graphene. Double layer graphene, has a different conductance behaviour with a broader dip, better known as an energy gap.

According to the team, in the presence of an electric field perpendicular to it, the energy gap makes double layer graphene more similar to the current tuneable semiconductors.

Peggy Lee

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