Optical and magneto-optical far-infrared properties of bilayer graphene

We analyze the spectroscopic features of bilayer graphene determined by the formation of pairs of low-energy and split bands in this material. We show that the inter-Landau-level absorption spectrum in bilayer graphene at high magnetic field is much denser in the far-infrared range than that in monolayer material and that the polarization dependence of its lowest-energy peak can be used to test the form of the bilayer ground state in the quantum Hall-effect regime.

Figure 1

Absorption coefficient of bilayer and monolayer graphenes in the optical range of frequencies. Insets illustrate the quasiparticle dispersion branches in the vicinity of ${ϵ}_F$ and possible optical transitions.

Figure 2

(a) Allowed inter-LL transitions without trigonal warping effects. Dashed and dash-dotted lines indicate transitions in ${\ell }_{\oplus }$ and ${\ell }_{\ominus }$ polarizations, respectively. (b) Monolayer (top) and bilayer (bottom) FIR absorption spectra in ${\ell }_{\oplus }$ and ${\ell }_{\ominus }$ polarizations for $B=10\mathrm{T}$ and filling factor $\nu =0$. Dashed and solid lines describe absorption by ferro- and antiferromagnetic states of the $\nu =0$ bilayer. (c) Weak field, $B=1\mathrm{T}$ magnetoabsorption in bilayer graphene with $\nu =0$ calculated with $({\upsilon }_3=0.2\upsilon )$ and without (${\upsilon }_3=0$, shaded) warping term in the Hamiltonian.