Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) have studied the dynamics of electrons from the "wonder material" graphene in a magnetic field for the first time. This led to the discovery of a seemingly paradoxical phenomenon in the material. Its understanding could make a new type of laser possible in the future. Together with researchers from Berlin, France, the Czech Republic and the United States, the scientists precisely described their observations in a model and have now published their findings in the scientific journal Nature Physics.
Graphene is considered a "wonder material": its breaking strength is higher than steel and it conducts electricity and heat more effectively than copper. As a two-dimensional structure consisting of only a single layer of carbon atoms, it is also flexible, nearly transparent and approximately one million times thinner than a sheet of paper. Furthermore, shortly after its discovery ten years ago, scientists recognized that the energy states of graphene in a magnetic field -- known as Landau levels -- behave differently than those of semiconductors. "Many fascinating effects have been discovered with graphene in magnetic fields, but the dynamics of electrons have never been studied in such a system until now," explains physicist Dr. Stephan Winnerl from HZDR.
The HZDR researchers exposed the graphene to a four-Tesla magnetic field -- forty times stronger than a horseshoe magnet. As a result, the electrons in graphene occupy only certain energy states. The negatively charged particles were virtually forced on tracks. These energy levels were then examined with free-electron laser light pulses at the HZDR. "The laser pulse excites the electrons into a certain Landau level. A temporally delayed pulse then probes how the system evolves," explains Martin Mittendorff, doctoral candidate at the HZDR and first author of the paper.
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