Magnetic field driven ambipolar quantum Hall effect in epitaxial graphene close to the charge neutrality point

Abstract : We have investigated the disorder of epitaxial graphene close to the charge neutrality point (CNP) by various methods: (i) at room temperature, by analyzing the dependence of the resistivity on the Hall coefficient; (ii) by fitting the temperature dependence of the Hall coefficient down to liquid helium temperature; (iii) by fitting themagnetoresistances at low temperature. All methods converge to give a disorder amplitude of (20±10) meV. Because of this relatively low disorder, close to the CNP, at low temperature, the sample resistivity does not exhibit the standard value~h/4e^2 but diverges. Moreover, themagnetoresistance curves have a unique ambipolar behavior,which has been systematically observed for all studied samples.This is a signature of both asymmetry in the density of states and in-plane charge transfer. The microscopic origin of this behavior cannot be unambiguously determined. However, we propose a model in which the SiC substrate steps qualitatively explain the ambipolar behavior.
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Abir Nachawaty, M. Yang, Wilfried Desrat, Sébastien Nanot, B. Jabakhanji, et al.. Magnetic field driven ambipolar quantum Hall effect in epitaxial graphene close to the charge neutrality point. Physical Review B : Condensed matter and materials physics, American Physical Society, 2017, 96 (7), pp.075442. ⟨10.1103/PhysRevB.96.075442⟩. ⟨hal-01584484⟩

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