Fano resonance of optical phonons in a multilayer graphene stack

We studied Fano interference between the Raman spectrum of G-band phonons and electron continuum in a multilayer graphene stack. The thickness and power dependencies of the Fano interference coefficient divide 1/q divide in the G-mode, where q is the Fano asymmetry parameter, were spatially visualized and analyzed using the Gaussian-convoluted Breit-Wigner-Fano function. The estimated divide 1/q divide decreases with an increase in the layer number and laser power in the low-power region at least for monolayer, bilayer, and trilayer graphene. In the higher-power region, divide 1/q divide increases with power only for monolayer graphene. The observed behaviors of divide 1/q divide reflect the phase difference of Raman signals from the electron continuum and G-band and possibly originate from changes in the electronic relaxation time and the Fermi level of graphene owing to the laser heating of the sample.