Carrier dynamics in Landau-quantized graphene featuring strong Auger scattering
Résumé
The energy spectrum of common two-dimensional electron gases consists of a harmonic, i.e. equidistant ladder of Landau levels, thus preventing the possibility to optically address individual transitions. In graphene, however, due to its non-harmonic spectrum, individual levels can be addressed selectively. We report here the first 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. In agreement with our experimental results, an analysis based on 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. Such a phenomenon has never been observed before in any system to our knowledge. 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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