Probing LO phonons of graphene under tension via the 2D′ Raman mode

Abstract

We use ab initio simulations and perturbation theory to study the 2D′ Raman mode of graphene subject to biaxial and uniaxial strains up to 2%. We demonstrate that 2D′ Raman measurements, as a function of polarization and laser energy EL, can probe the LO phonons of graphene with arbitrary radial and angular extent around Γ. The 2D′ profile is highly sensitive to uniaxial strain and depends on both polarization and strain orientation. The Grüneisen parameter γ2D′≈1.71 has a mild dependency on the laser energy EL, and is found to be in good agreement with experiments and comparable in value to γG. The shear deformation potential β2D′ depends strongly on the polarization and strain orientation, becoming negative when the polarizer and analyzer are perpendicular to each other. Finally, we describe a robust method to determine the uniaxial strain by relying solely on polarized measurements of the 2D′ mode.