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Optical properties of carbon based materials in high magnetic fields

Carbon nanotubes are unique nano-objects with highly anisotropic electrical, magnetic and optical properties. In the past years the physics of carbon nanotubes made important steps toward the comprehension of its various complex physical properties. The optical response of nanotubes is driven by excitons. Of the sixteen possible exciton states only one decays radiatively. However a magnetic field can brighten one of the dark states. The aim of the first part of this thesis investigates the issue of the brightening of dark excitons. In the second part we use the magnetic properties of single walled carbon nanotubes to investigate their dynamic alignment in a pulsed magnetic field. Semiconducting tubes are diamagnetic both along and perpendicular to their long axis but the magnitude of the perpendicular susceptibility is higher. Metallic tubes are paramagnetic along their long axis and diamagnetic perpendicular to it. This constrains SWNT to align parallel to a magnetic field. Our data will be analysed with the aid of a theoretical model based on rotational diffusion of rigid rods. In the third part we study the magneto-optical properties of epitaxially grown multi-layer graphene. The Landau levels of graphene are different from standard two dimensional electron gases. They show a pB-dependence due to the relativistic nature of their charge carriers. We measure the system at high fields and high energies to probe the limit of massless Dirac fermions. The discovery of massless relativistic particles in graphene, a mono-layer of graphite, has completely renewed the interest in graphite. As a matter of fact graphite the optical properties of graphite are best described by bi-layer graphene. We show that the magneto-transmission experiments on thin graphite are in very good agreement with an effective bi-layer model. In addition we observe a non-predicted double structure in the graphene-like transitions which is not reported before.