Anisotropic phonon softening of uniaxially strained bilayer graphene

The effect of strain on the phonon dispersion of bilayer graphene has been studied by polarized Raman spectroscopy on uniaxially strained bilayer graphene. Each of the four peaks that constitute the Raman 2D band splits and redshifts under strain, with the shift rate depending on the strain direction relative to the crystallographic orientation. By comparing the experimental data with first-principles calculation results, it is shown that the splitting and the redshift of the peaks originate from the anisotropic modifications of the phonon dispersion and the electronic band structure of bilayer graphene. The intensity of each peak also depends on the magnitude and direction of strain, which can be explained in terms of the correlation with the momentum of the phonon involved in the Raman scattering path.