Optical properties of carbon based materials in high magnetic fields Jury

Carbon nanotubes are unique nano-objects with highly anisotropic electrical, mag-netic and optical properties. In the past years the physics of carbon nanotubesmade important steps toward the comprehension of its various complex physicalproperties. The optical response of nanotubes is driven by excitons. Of the sixteenpossible exciton states only one decays radiatively. However a magnetic field canbrighten one of the dark states. The aim of the first part of this thesis investigatesthe issue of the brightening of dark excitons.In the second part we use the magnetic properties of single walled carbon nanotubesto investigate their dynamic alignment in a pulsed magnetic field. Semiconduct-ing tubes are diamagnetic both along and perpendicular to their long axis but themagnitude of the perpendicular susceptibility is higher. Metallic tubes are param-agnetic along their long axis and diamagnetic perpendicular to it. This constrainsSWNT to align parallel to a magnetic field. Our data will be analysed with the aidof a theoretical model based on rotational diffusion of rigid rods.In the third part we study the magneto-optical properties of epitaxially grownmulti-layer graphene. The Landau levels of graphene are different from standardtwo dimensional electron gases. They show a√B-dependence due to the relativis-tic nature of their charge carriers. We measure the system at high fields and highenergies 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 theoptical properties of graphite are best described by bi-layer graphene. We show thatthe magneto-transmission experiments on thin graphite are in very good agreementwith an effective bi-layer model. In addition we observe a non-predicted doublestructure in the graphene-like transitions which is not reported before.tel-00646148,version1-29Nov2011 Auteur: Nicolas UBRIGTitre: Propriétés optiques des matériaux à base de carbone sous champ magnétiqueintenseDirecteurs de thèse: Geert RIKKEN et Oliver PORTUGALLSpécialité: Physique Lieu et date de la soutenance: Salle de séminaire du LNCMI, 18 Mars2011Laboratoire: Laboratoire National des Champs Magnétiques Intenses (LNCMI),CNRS-UPR 3228, 143 Avenue de Rangueil, 31400 Toulouse