  Under homogeneous uniaxial strains, the Raman 2D band of graphene involving
two-phonon double-resonance scattering processes splits into two peaks and they
altogether redshift strongly depending on the direction and magnitude of the
strain. Through polarized micro- Raman measurements and first-principles
calculations, the effects are shown to originate from significant changes in
resonant conditions owing to both the distorted Dirac cones and anisotropic
modifications of phonon dispersion under uniaxial strains. Quantitative
agreements between the calculation and experiment enable us to determine the
dominant double- resonance Raman scattering path, thereby answering a
fundamental question concerning this key experimental analyzing tool for
graphitic systems.
