Quantum pathways inducing coherent lattice dynamics are studied in bismuth (Bi). A crystalline Bi film is excited by femtosecond midinfrared pulses and transient intensity changes on the (111) Bragg reflection are probed by hard x-ray pulses. A fast decrease and coherent oscillations of the diffracted intensity display up to 50% and 10% intensity change, respectively. The oscillation frequency of 2.6 THz is independent of pump intensity. Midinfrared excitation opens different quantum pathways for electron-hole generation, such as field-driven carrier tunneling at the $L$ points, which reduces the crystal symmetry and leads to optical phonon excitation at the $X$ point with the strongest electron-phonon coupling.

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• Anharmonic lattice dynamics
• Lattice dynamics
• Optical phonons
• Elemental materials
• Narrow band gap systems
• Semimetals
• Single crystal materials
• Time-resolved infrared spectroscopy
• Ultrafast femtosecond pump probe
• X-ray diffraction