Electron–phonon coupling and defect scatterings in Ar⁺-ion implanted graphite

Abstract

Dynamics of coherent G-mode and D-mode phonons in Ar⁺-ion implanted graphite has been investigated using transient reflectivity measurement. With an increase in the Ar⁺-ion dose, coherent D-mode phonon appears at which the dephasing rate of the coherent G-mode phonon begins to increase. The increase in the amplitude of the coherent D-mode phonon and those in dephasing rates of the coherent D-mode and G-mode phonons indicate effective carrier-defect scatterings in the defective graphite. The dephasing rate of the D-mode is larger than that of the G-mode, indicating an existence of an additional dephasing process for the D-mode. We attribute it to the broad spectral distribution of the D-mode phonon, which is understood as a coherent excitation of large wavevector phonons with different wavevectors through inter-Dirac-cone scattering. The frequency chirping of the D-mode and its defect density dependence are also discussed based on this scattering mechanism.