Figure 1

Left-hand panel: Dipole allowed transitions in a neutral graphene sheet in the presence of an external magnetic field. The horizontal lines denote the unevenly spaced Landau levels of massless Dirac fermions. The filled valence band levels ($\lambda =-1$) and the empty conduction band levels ($\lambda =+1$) are indicated by filled (empty) circles. The zero-energy ($n=0$) Landau level is formed partly from the valence band and partly from the conduction band and is half filled in a neutral system. Right-hand panel: In a doped graphene sheet with a Fermi level ${\epsilon }_F$ placed between the conduction band $n=M$ and the $n=M+1$ Landau levels, there is an allowed cyclotron transition within the conduction band (magenta arrow) while some of the lower energy interband transitions, indicated by dashed lines, are Pauli blocked. There is a clear energetic separation between the lowest energy (unblocked) intraband transition and the (unblocked) interband transitions.Reuse & Permissions