The energy spectrum of common two-dimensional electron gases consists of a harmonic (that is, equidistant) ladder of Landau levels, thus preventing the possibility of optically addressing individual transitions. In graphene, however, owing to its non-harmonic spectrum, individual levels can be addressed selectively. Here, we report a time-resolved experiment directly pumping discrete Landau levels in graphene. Energetically degenerate Landau-level transitions from n = −1 to n = 0 and from n = 0 to n = 1 are distinguished by applying circularly polarized THz light. An analysis based on a microscopic theory shows that the zeroth Landau level is actually depleted by strong Auger scattering, even though it is optically pumped at the same time. The surprisingly strong electron–electron interaction responsible for this effect is directly evidenced through a sign reversal of the pump–probe signal.
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Support from the German Science Foundation DFG in the framework of the Priority Program 1459 Graphene is acknowledged. E.M. and F.W. are grateful to the Einstein Foundation Berlin. The research at the free-electron laser FELBE was supported by the European Community’s Seventh Framework Programme (FP7/2007–2013) under Grant agreement No. 226716. Part of this work has been supported by the ERC-2012-AdG-320590 MOMB project as well as the EC Graphene Flagship. We are grateful to P. Michel and the FELBE team for their dedicated support. The Grenoble group acknowledges fruitful discussions with D. M. Basko.
The authors declare no competing financial interests.
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Mittendorff, M., Wendler, F., Malic, E. et al. Carrier dynamics in Landau-quantized graphene featuring strong Auger scattering. Nature Phys 11, 75–81 (2015). https://doi.org/10.1038/nphys3164
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