Propriétés électroniques du graphène épitaxié proche de point de neutralité de charge

Abstract : Local and nonlocal magnetoresistances measurements on monolayer graphene grown on the silicon face of silicon carbide (SiC) are reported. The purpose of this work is to understand the physical phenomena appearing close to the charge neutrality point in these monolayers. The first issue to overcome was that graphene is generally strongly doped with electrons due to the interaction with the substrate. The control of the Fermi level has been realised using the corona discharge method. The disorder amplitude has been evaluated in these structures by : (i) fitting the resistivity dependence curve of the Hall coefficient obtained at room temperature; (ii) fitting the temperature dependence of the Hall density for samples that were prepared near the charge neutrality point. All these analyses gave a disorder strength equal to (20 ± 10) meV. It is then shown that for samples with low hole doping, the Hall resistance exhibits an ambipolar behavior as a function of the magnetic field. This behavior is accompanied by the appearance of a local maximum in the longitudinal resistance.This behavior is been explained by a charge transfer model between regions of different doping in graphene. Nevertheless, the microscopic origin of these regions is poorly known. Finally, nonlocal measurements carried out on these samples showed the appearance of important nonlocal resistances which in some cases exceed the corresponding longitudinal resistances. The analysis of these results shows that the contribution of spin current and thermal effects on the occurrence of these nonlocal voltages is neglegible. In contrast, the experimental data are reproduced quite well by a model based on counter-propagating edge states backscattered by the bulk.
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Abir Nachawaty. Propriétés électroniques du graphène épitaxié proche de point de neutralité de charge. Physique [physics]. Université Montpellier, 2018. Français. ⟨NNT : 2018MONTS095⟩. ⟨tel-02157943⟩

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