Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

To investigate the carrier relaxation dynamics in Landau quantized graphene, we performed pump-probe measurements on quasi-neutral sheets of multilayer epitaxial graphene in magnetic fields. Due to the linear dispersion for low energies in graphene, the Landau level (LL) spacing is not equidistant. Hence it is possible to investigate a single LL transition selectively. To this end we performed pump-probe measurements at a wavelength of 16.5 µm and applied a magnetic field of up to 7T. We varied the magnetic field for resonant measurements at three different LL transitions. For the transitions LL-1(-2) -> LL2(1) and LL-2(-3) -> LL3(2) we could observe a slight increase of the pump-probe signal while the relaxation time stayed constant. For the transition LL-1(0) -> LL0(1) the amplitude of the pump-probe signal increased by a factor of 2.5, the relaxation time decreased from 20 ps to 5 ps. To understand the processes, influencing the carrier relaxation, we performed measurements with linearly and circularly polarized radiation. This enables us to distinguish between the transition LL-1->LL0 and LL0->LL1. This revealed complex dynamics involving positive and negative signals. We suggest this to result from different relaxation channels including Auger processes.