Coulomb-mediated crosstalk between selection-rule separated pairs of Landau-level transitions in graphene

We investigate the carrier dynamics in the system of Landau-levels LL-2, LL-1, LL1, and LL2 of multi-layer graphene on SiC at 10 K. We perform degenerate pump-probe experiments at 75 meV with circularly polarized radiation addressing the transitions LL-2 → LL1 and LL-1 → LL2 selectively. In the co-polarized configurations, we observe bleaching of the LL-2 → LL1 and LL-1 → LL2 transition, respectively. We discuss the dependence of scattering on the number of photoexcited carriers. The existence of a pump-probe signal in cross-polarized configurations points towards thermalization of carriers across the Landau ladder on a ps timescale.