Electronic and Phonon Instabilities in Bilayer Graphene under Applied External Bias

Abstract

We have performed electronic-structure and lattice-dynamics calculations on the AB and AA structures of bilayer graphene. We study the effect of external electric fields and compare results obtained with different levels of theory to existing theoretical and experimental results. Application of an external field to the AB bilayer alters the electronic spectrum, with the bands changing under bias from a parabolic to a "Mexican hat" double-well structure. This results in a semi-metal-to-semiconductor phase transition, with the size of the induced electronic band-gap being tuneable through the field strength. A reduction of continuous symmetry from a hexagonal to a triangular lattice is also evidenced through in-plane electronic charge inhomogeneities between the sublattices. When spin-orbit coupling is turned on for the AB system, we find that the bulk gap decreases, gradually increasing for larger intensities of the bias. Under large bias the energy dispersion recovers the Mexican hat structure, since the energy interaction between the layers balances the coupling interaction. We find that external bias perturbs the harmonic phonon spectra and leads to anomalous behaviour of the out-of-plane flexural ZA and layer-breathing ZO' modes. For the AA system, the electronic and phonon dispersions both remain stable under bias, but the phonon spectrum exhibits zone-center imaginary modes due to layer-sliding dynamical instabilities.

arXiv commentSubmitted to Materials Today: Proceedings (ANM2018)

References in corpus (17)

• Ultrathin epitaxial graphite: 2D electron gas properties and a route toward graphene-based nanoelectronics
• Biased bilayer graphene: semiconductor with a gap tunable by electric field effect
• Unconventional quantum Hall effect and Berry's phase of 2pi in bilayer graphene
• Asymmetry gap in the electronic band structure of bilayer graphene
• Phonon-phonon interactions in transition metals
• The phonon dispersion of graphite by inelastic x-ray scattering
• Thermal physics of the lead chalcogenides PbS, PbSe, and PbTe from first principles
• Accuracy of generalized gradient approximation functionals for density functional perturbation theory calculations
• Two-Dimensional Topological Insulator State and Topological Phase Transition in Bilayer Graphene
• A Review on Flexural Mode of Graphene: Lattice Dynamics, Thermal Conduction, Thermal Expansion, Elasticity, and Nanomechanical Resonance
• Instabilities of the AA-stacked graphene bilayer
• Electronic Liquid Crystalline Phases in a Spin-Orbit Coupled Two-Dimensional Electron Gas
• AA-stacked bilayer graphene in an applied electric field: Tunable antiferromagnetism and coexisting exciton order parameter
• Bound state energy of a Coulomb impurity in gapped bilayer graphene: "Hydrogen atom with a Mexican hat"
• Persistent Current States in Bilayer Graphene
• Wigner crystal phases in bilayer graphene
• Electric bias control on impurity effects in bigraphene