Attosecond extreme-ultraviolet (XUV) transient absorption spectroscopy measurements on the Peierls-distorted phase of the semimetal antimony (Sb) are presented. After excitation by an ultrashort, broad band near-infrared (NIR) pulse, the distortion is (partly) lifted causing the well-known coherent phonon motion of the lattice. While the overall observed dynamics generally follow a displacive excitation model, a delayed onset of the pump-induced carrier dynamics because of hot-carrier thermalization is observed, as well as a large spectral phase dependence in the coherent phonon oscillation. This is attributed to significantly different carrier relaxation timescales for carrier energies above and near the Fermi level of the semimetal and corroborated by a simple theoretical model that considers the carrier relaxation timescales in the displacive phonon model to explain the observed dynamics. Our results provide direct experimental evidence about the role of carrier-relaxation in the origin of displacive coherent phonon motion.

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• Electron relaxation
• Electron-phonon coupling
• Electronic structure
• Optical phonons
• Ultrafast phenomena
• Semimetals
• Attosecond laser spectroscopy
• Transient absorption spectroscopy