Effect of a magnetic field on the two-phonon Raman scattering in graphene

We have studied, both experimentally and theoretically, the change in the so-called 2D band of the Raman-scattering spectrum of graphene (the two-phonon peak near 2700 cm(-1)) in an external magnetic field applied perpendicular to the graphene crystal plane at liquid-helium temperature. A shift to lower frequency and broadening of this band is observed as the magnetic field is increased from 0 to 33 T. At fields up to 5-10 T, the changes are quadratic in the field while they become linear at higher magnetic fields. This effect is explained by the curving of the quasiclassical trajectories of the photoexcited electrons and holes in the magnetic field, which enables us (i) to extract the electron inelastic-scattering rate and (ii) to conclude that electronic scattering accounts for about half of the measured width of the 2D peak.