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Magneto-phonon resonance

Our low-temperature magneto-Raman scattering measurements performed on graphene-like locations on the surface of bulk graphite, carries the energyite reveal a new series of magneto-phonon resonances involving both K point and Γ point phonons. These are resonances between a purely electronic excitation, an electronic excitation accompanied by one phonon, and a two-phonon excitation. In particular, we observe the resonant splitting of three crossing excitation branches. We give a detailed theoretical analysis of these multi-excitation resonances. Our results highlight the role of combined excitations and the importance of multi-phonon processes (from both K and Γ points) for the relaxation of hot carriers in graphene.

 

Fig. 1: (left) This schematics illustrate the possible resonances between the electronic excitation spectrum in magnetic field, and phonons of graphene. The horizontal lines represent the Landau levels, the black circles represent their filling. The filled red circles represent the excited electrons, the vertical arrows show their transitions which are resonant with a phonon. (right) Magnetic field dependence of the main features observed in our Raman scattering spectra. Red points indicate resonances involving K-point phonons, blue point indicate resonances involving Γ-point phonons and orange points indicate the effects of the E1,n(-n,-1) = EK resonance. Green circles represent the case (iii) resonance with z = 2 observed on the L-3,4 excitation. The horizontal gray barmasks the residual contribution of the 2D band.

 

More details in D.M. Basko et al., 2D Materials 3, 015004, (2016)