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Observation of fast Auger scattering in Landau-quantized graphene

Graphene subject to the external magnetic field, with its electronic states quantized into a discrete Landau levels, represents a natural playground to study interactions among charged Dirac-type carriers. Fractional quantum Hall effect, nowadays widely explored in both graphene monolayer and bilayer, is the most representative demonstration of such correlated-electron phenomena.
A recent publication, resulting from an international collaboration of researchers from Germany, France, and USA, reports on another manifestation of electron-electron interaction in Landau-quantized graphene, this time observed in a purely optical experiment. Exciting electrons between Landau levels by pulsed infrared laser, time-resolved spectroscopy (pump-probe technique) allowed the researchers to study mechanisms of carrier relaxation back to thermal equilibrium. Among them, surprisingly fast Auger processes (electron-electron scattering) have been identified. Such processes are well-known and studied in conventional materials, nevertheless, they were originally expected to vanish in graphene due to its specific non-equidistant spacing of Landau levels. Understanding such efficient Auger scattering in graphene represents a basic prerequisite for possible construction of Landau level laser on Dirac-type electrons – theoretically predicted widely tunable source of infrared radiation.
 
 
Fig. 1 : Relative changes of graphene’s transmission induced by a picosend pulse of infrared radiation for various magnetic fields. In the inset, the pump–probe experiment is schematically depicted.
 
 
 
Reference :
M. Mittendorff, F. Wendler, E. Malic, A. Knorr, M. Orlita, M. Potemski, C. Berger, W. A. de Heer, H. Schneider, M. Helm and S. Winnerl, Nature Physics, aop (2014), doi :10.1038/nphys3164
Contact :
Stephan Winnerl & Martin Mittendorff, HZ Dresden-Rossendorf (s.winnerl@hzdr.de)
Milan Orlita, LNCMI-CNRS, Grenoble (milan.orlita@lncmi.cnrs.fr)