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Structure de bandes et transport électronique dans les nanotubes de carbone sous champ magnétique intense

Abstract : Electronic transport measurements in individual multiwall carbon nanotubes under pulsed magnetic field (60T) are presented in this PhD thesis. The purpose is to observe modulations of the electronic dispersion by the magnetic field. High quality nanotubes are contacted with short distances between contacts. This allows to reach quasi-ballistic and slightly diffusive transport regimes occurring mainly on the outer wall. Transistor configuration enables to modulate the charge carrier energy (Fermi level) through many subbands by an electrostatic potential (“a gate”). In order to clarify the contribution of innermore shells, a spectroscopic Raman study is first presented. A strong variation from wall to wall of the intensity of charge transfer between successive shells is unraveled. The study under magnetic field of nanotubes with semiconducting and metallic outer wall is then presented. When the magnetic field is applied perpendicularly to the axis of the nanotube, the onset of propagating Landau states is unveiled. This induces modulations of resonance conditions in an electronic Fabry-Pérot type regime, closing of the energy gap in a semiconducting shell and reintroduction of backscattering in a metallic one. This last effect comes with a pinning of the Fermi level to the Landau one gathering at zero energy under high field. Those results are in agreement with theoretical models taking into account an homogeneous disorder. Finally, the Aharonov-Bohm effect under many periods and many subbands is observed when the field is parallel to the axis of the nanotube. The metallicity of the outer wall and the correspondence between the gate voltage and the charge carrier energy are obtained by comparing the experimental conductance oscillations with a model obtained in the perfect case. To describe further the magneto-fingerprints, transmission lowering at the contacts and due to defects are qualitatively considered.
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Contributor : Sebastien Nanot <>
Submitted on : Thursday, February 4, 2010 - 11:34:29 PM
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  • HAL Id : tel-00453517, version 1


Sebastien Nanot. Structure de bandes et transport électronique dans les nanotubes de carbone sous champ magnétique intense. Physique [physics]. Université de Toulouse; Université Paul Sabatier - Toulouse III, 2009. Français. ⟨tel-00453517⟩



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