Ultrafast spectroscopy on Landau quantized graphene: Evidence for strong Auger scattering

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 terahertz radiation (at 20 THz) allows one to excite the two energetically degenerate transitions LL-1 → LL0 and LL-1 → LL0, respectively, selectively. Surprisingly, induced transmission is observed in one configuration of pumping and probing with opposite configuration. 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.