Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

While the carrier dynamics in graphene in absence of magnetic fields is well researched in a large spectral range ranging from UV to THz, the dynamics in Landau quantized graphene is almost unexplored. We investigate the carrier dynamics within the system of Landau levels (LLs) of index n = -1, n = 0 and n = 1 by pump-probe experiments complemented by microscopic modelling. Using circularly polarized mid-infrared radiation (photon energy 75 meV) allows one to selectively excite the two energetically degenerate transitions LL-1 → LL0 and LL-1 → LL0, respectively. Surprisingly, induced transmission is observed in one configuration of pumping and probing with opposite configuration (cf. Fig 1 (c) and (d)). Considering single particle Pauli blocking, one would expect induced absorption in this case. The sign change indicates that LL0 is depleted by strong Auger scattering, even though it is optically pumped at the same time.
We discuss the role of carrier-carrier and carrier-phonon scattering in Landau quantized graphene and provide an outlook on the application potential of this system for tunable THz lasers.

References
[1] 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 Phys. 11, 75 (2015).