Carbon atoms can form bonds in many different ways. Pure carbon can come in many forms, including diamond, graphite, nanotubes, soccer-ball-shaped molecules, or a honeycomb grid of hexagonal cells known as graphene. This exotic, strictly two-dimensional material perfectly conducts electricity, but is not a superconductor. Perhaps this will change soon.
Scientists at the BESSY II Research Center can scan the so-called stripe structure of a sample. This strip structure provides information on how charge carriers are distributed in quantum-mechanically allowed states and which charge carriers are generally available for transport. Angle Resolved Photoemission Spectroscopy (ARPES) in BESSY II allows such measurements to be made with extremely high resolution.
Through precise analysis of the stripe structure, the scientists identified an area that they had not seen before. “The double layer of graphene has been studied before, because it is a semiconductor with a band gap,” explains scientist Andrei Varikhalov. “But the ARPES tool in BESSY II is high enough resolution to see a flat area near the bandgap.”
This flat band is a prerequisite for superconductivity, but only if it matches the so-called Fermi energy. In the case of bilayer graphene, its energy level is only 200 millielectronvolts lower than the Fermi energy, but the energy level of the flat region can be raised to the Fermi energy by doping with foreign atoms or applying an external voltage, the so-called gate voltage.
Perhaps physicists will find a way to turn this wonder material into a superconductor. And if you’re lucky, then a superconductor that works at room temperature.
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