Relaxation dynamics in graphene close to the Dirac point

The carrier dynamics in epitaxially grown graphene is studied in pump-probe experiments with photon energies in the range from 10 – 250 meV. A strong increase of the relaxation time is observed as the photon energy is decreased to values below the optical phonon energy. The underlying processes dominating the relaxation are identified by a comparison of the experimental results with microscopic calculations. Variation of the photon energy between 20 meV and 30 meV results in a change from induced transmission for larger photon energies to induced absorption for lower photon energies. An interplay of interband and intraband processes is responsible for this behavior.