Chemistry Reference
In-Depth Information
Fig. 20. G mode spectra of top gated bilayer graphene for different top gate voltages.
Lines are Lorentzian fit to the experimental data denoted by squares. The dotted line
shows the evolution of the lower mode.
Note, that that the Dirac point voltage is
subtracted from applied voltages.
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phonon are the eigenstates of the bilayer.
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However, as the bilayer is
doped either with electrons or with holes, owing to the existence of an inter-
layer electric field, the inversion symmetry is broken, mixing the symmetric
and the antisymmetric modes. The breaking of this inversion symmetry
is manifested in the splitting of Raman G mode, with energy and spectral
weight evolving as the doping increases.
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Figure 20 shows the bilayer
G band splitting as a function of top gate voltage in our experiments.
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The resulting phonon eigenstates can be viewed as a superposition of both
the in-phase and out-of-phase displacements and both the modes become
Raman active. Near the charge neutral point, Raman G peak is a single
line peak which is attributed to the in-phase motion of the two layers.
As the doping increases, the separation between the two bands widens,
