title: Asymmetric bandgaps and Landau levels in a Bernal-stacked hexagonal boron-nitride bilayer.
abstract: A Bernal-stacked hexagonal boron-nitride (h-BN) bilayer is a two-dimensional polar crystal. Within the tight-binding approximation, we investigate the band structure of a gated h-BN bilayer by analyzing the density of states and the behavior of the charge transfer. We find that the bandgaps of the h-BN bilayer vary asymmetrically under two opposite biases due to asymmetric changes of the interlayer and intralayer polarities. We also find that the bias-driven net charge transfer between layers can be up to 0.2 electron per unit cell. Under the bias along one direction, the system exhibits quantum phase transitions from a semiconductor to a semimetal and then to a semiconductor again, whereas under the reverse bias, the system is always semiconducting. Besides, asymmetric Landau levels under opposite biases arise in the presence of a magnetic field. Moreover, dispersive edge states are found to exist in the bulk bandgap for an h-BN bilayer nanoribbon under the bias along one direction, which does not happen when the bias is reversed. All these properties of h-BN bilayers are measurable in transport experiments.
authors.affiliation: National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing, 210093, People's Republic of China.
authors.forename: Xuechao
authors.initials: X
authors.lastname: Zhai
authors.forename: Guojun
authors.initials: G
authors.lastname: Jin
mesh_terms: D001896:Boron Compounds / Q000737:chemistry*; D004583:Electrons; D060526:Magnetic Fields; D049329:Nanostructures / Q000737:chemistry*; D044367:Phase Transition; D011789:Quantum Theory; D012666:Semiconductors; D013499:Surface Properties
chemical_list: D001896:Boron Compounds; C017282:boron nitride