Quantum Hall effect in biased bilayer grapheneR. Ma1, 2, L. J. Zhu2, L. Sheng3, M. Liu1 and D. N. Sheng2
1 Department of Physics, Southeast University - Nanjing 210096, China
2 Department of Physics and Astronomy, California State University - Northridge, CA 91330, USA
3 National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University Nanjing 210093, China
received 10 May 2009; accepted in final form 25 June 2009; published July 2009
published online 24 July 2009
We numerically study the quantum Hall effect in biased bilayer graphene based on a tight-binding model in the presence of disorder. Integer quantum Hall plateaus with quantized conductivity (where is an integer) are observed around the band center due to the split of the valley degeneracy by an opposite voltage bias added to the two layers. The central (n = 0) Dirac-Landau level is also split, which leads to a pronounced = 0 plateau. This is consistent with the opening of a sizable gap between the valence and conduction bands. The exact spectrum in an open system further reveals that there are no conducting edge states near zero energy, indicating an insulator state with zero conductance. Consequently, the resistivity should diverge at the Dirac point. Interestingly, the = 0 insulating state can be destroyed by disorder scattering with intermediate strength, where a metallic region is observed near zero energy. In the strong-disorder regime, the Hall plateaus with nonzero are destroyed due to the float-up of extended levels toward the band center and higher plateaus disappear first.
73.43.Cd - Theory and modeling.
72.10.-d - Theory of electronic transport; scattering mechanisms.
72.15.Rn - Localization effects (Anderson or weak localization).
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