QHE and far infra-red properties of bilayer graphene in a strong magnetic field.

We describe the quantum Hall effect (QHE) and far infra-red (FIR) absorption properties of bilayer graphene in a strong magnetic field and contrast them with the weak field regime. This includes a derivation of the effective low energy Hamiltonian for this system and the consequences of this Hamiltonian for the sequencing of the Landau levels in the material: The form of this effective Hamiltonian gives rise to the presence of a level with doubled degeneracy at zero energy. The effect of a potential difference between the layer of a bilayer is also investigated. It is found that there is a density-dependent gap near the K points in the band structure. The consequences of this gap on the QHE are then described. Also, the magneto-absorption spectrum is investigated and an experiment proposed to distinguish between model ground states of the bilayer quantum Hall effect system based on the different absorption characteristics of right-handed and left-handed polarisation of FIR light. Finally, the effects of trigonal warping are taken into account in the absorption picture