Landau-level degeneracy and quantum Hall effect in a graphite bilayer.

We derive an effective two-dimensional Hamiltonian to describe the low-energy electronic excitations of a graphite bilayer, which correspond to chiral quasiparticles with a parabolic dispersion exhibiting Berry phase 2pi. Its high-magnetic-field Landau-level spectrum consists of almost equidistant groups of fourfold degenerate states at finite energy and eight zero-energy states. This can be translated into the Hall conductivity dependence on carrier density, sigma(xy)(N), which exhibits plateaus at integer values of 4e2/h and has a double 8e2/h step between the hole and electron gases across zero density, in contrast to (4n + 2)e2/h sequencing in a monolayer.