From the Integer to the Fractional Quantum Hall Effect in Graphene

The fractional quantum Hall effect is a very particular manifestation of electronic correlations in two-dimensional systems in a strong perpendicular magnetic field. It arises as a consequence of a strong Coulomb repulsion between electrons in the same Landau level that conspires with a particular chirality of the electronic states. This chirality is inherited from the classical cyclotron motion, i.e. a particular sense of electronic rotation due to the orientation of the magnetic field. The specificity of the FQHE in graphene consists of a four-fold spin-valley degeneracy inherited from the electronic bands in the vicinity of the Fermi level. The relevant Coulomb interaction respects this SU(4) symmetry, and one is therefore confronted with a generic four-component fractional quantum Hall effect, as well as with other correlated four-component phases, such as spin-valley ferromagnetic states. The present article aims at a -- mainly theoretical -- discussion of these exotic phases, in comparison with experimental evidence for them.