11 40 It is worth noticing that only the relative arrangement of the two electron trajectories and not their particular orientation with respect to the crystal axis are relevant in our consideration. This emphasizes the generality of our approach which is valid even if a specific direction for electronic momentum could be assumed to contribute to the 2D band Raman scattering signal in sp 2 carbon materials $^{13}$. 35 Actually, the contribution to γ from electron-electron col- lisions does acquire a B -dependent correction due to the curvature of the electronic trajectories. 30 However, when the sample is not strongly doped, it is reasonable to as- sume that the main source of electronic scattering is the 34 In fact, the assumption of the constant phonon density of states is not necessary, since one can use the phonon disper- sion in the vicinity of the K point which has been recently measured by inelastic x-ray scattering [A. Gr¨ uneis, J. Ser- rano, A. Bosak, M. Lazzeri, S.L. Molodtsov, L. Wirtz, C. Attaccalite, M. Krisch, A. Rubio, F. Mauri, and T. Pich- ler, Phys. Rev. B 80 , 085423, (2009)]. The theoretical curves in Fig. 2 were produced using this experimental dispersion. However, calculations with a constant phonon density of states lead to an almost similar result (within a few percent). 39 W.H. Reid, Zeitschrift f¨ ur Angewandte Mathematik und Physik 46 , 159, (1995). 38 P. Plochocka, C. Faugeras, M. Orlita, M.L. Sadowski, G. Martinez, M. Potemski, M.O. Goerbig, J.-N Fuchs, C. Berger, and W.A. de Heer, Phys. Rev. Lett. 100 , 087401, (2008). 37 C. Casiraghi, Phys. Rev. B 80 , 233407 (2009). 36 D.M. Basko, S. Piscanec, and A.C. Ferrari, Phys. Rev. B 80 , 165413, (2009). 33 O. Vall´ ee and M. Soares, Airy Functions and Applications to Physics (World Scientific, Hackensack, 2004). 32 P. Carmier and D. Ullmo, Phys. Rev. B 77 , 245413, (2008). 31 D.M. Basko, Phys. Rev. B 79 , 205428, (2009). 30 T.A. Sedrakyan, E.G. Mishchenko, and M.E. Raikh, Phys. Rev. Lett. 99 , 036401, (2007). 29 D.M. Basko, Phys. Rev. B 78 , 125418, (2008). 28 M.O. Goerbig, J.-N Fuchs, K. Kechedzhi, and V.I. Falko, Phys. Rev. Lett. 99 , 087401, (2007). 27 T. Ando, J. Phys. Soc.Jpn. 76 , 024712, (2007). emission of phonons. The corresponding rate depends on the magnetic field through the electronic density of states. The latter developes oscillations whose amplitude is ex- ponentially small for the non-quantizing field, and the ef- fect analyzed in the paper is indeed the dominant one. For quantizing magnetic fields, the electronic density of states is dominated by Landau levels, which should then be taken into account.