Étude des propriétés électroniques du graphène et des matériaux à base de graphène sous champs magnétiques intenses

Abstract : This thesis presents transport measurement on two-dimensional and uni-dimensional graphene-based systems under pulsed magnetic field (60T). The objective of this work is to probe the dynamics of charge carriers by changing the density of states of the system by applying a magnetic field. The first part is devoted to the study of the influence of electron-hole pockets on the transport properties of graphene near the charge neutrality point. We found the appearance of fluctuations in the magnetoresistance due to the progressive transition of the electrons/holes puddles of finite size in the quantum regime when the magnetic field increases. We have also shown that the variation of the Fermi energy, due to the increase of orbital Landau levels degeneracy, is directly responsible of a change in the electrons and holes ratio. The second part is devoted to the study of graphene nanoribbons, we explored two different width range. In the broad ribbons (W> 60 nm), quantification of the resistance is observed, revealing a clear signature of the quantization of the energy spectrum into Landau levels. We show for the first time the valley degeneracy lifting induce by the magnetic confinement of charge carriers at the edges of armchair nanoribbons. For narrower ribbons (W <30 nm) in presence of edge defects and charged impurities, the progressive formation of chiral edge states leads to a positive magneto-conductance whatever the carrier density. The last part deals with the magneto-transport in multi-sheet graphene. We observed the quantum Hall effect in tri-layer graphene. A comparative study of experimental results with numerical simulations was used to determine the rhombohedral stacking of three layers of graphene in the sample.
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Theses
Mesoscopic Systems and Quantum Hall Effect. INSA de Toulouse, 2011. French


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Submitted on : Tuesday, November 29, 2011 - 1:22:34 PM
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Jean-Marie Poumirol. Étude des propriétés électroniques du graphène et des matériaux à base de graphène sous champs magnétiques intenses. Mesoscopic Systems and Quantum Hall Effect. INSA de Toulouse, 2011. French. <tel-00646172>

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