Enhanced coherent phonon excitation in Fe3GeTe2 via resonance Raman effect

Coherent phonon excitation via femtosecond laser pulses can be used to control physical properties of matter, and enhancing coherent phonon excitation is highly relevant. Here, we report the strong enhancement of coherent phonon excitation in ${\mathrm{Fe}}₃{\mathrm{GeTe}}₂$ (FGT) via the resonance Raman effect. On the basis of the femtosecond transient optical spectroscopy measurements, the ${A}_{1\mathrm{g}}$ coherent phonon excitation in FGT is obtained as a function of pump photon energy. Its excitation can be maximized by tuning the pump photon energy. The maximum coherent phonon excitation at the 1.574-eV pump photon energy corresponds to an electronic transition in FGT, and is a direct result of the resonance Raman effect. The ${A}_{1\mathrm{g}}$ coherent phonon generation follows the impulsive stimulated Raman scattering mechanism. Our work demonstrates that the resonance Raman effect can be an effective way to enhance coherent phonon excitation via electronic excitation.