Terahertz-Induced Tunnel Ionization Drives Coherent Raman-Active Phonon in Bismuth

Area of Science:

• Quantum Materials Science
• Ultrafast Spectroscopy
• Solid-State Physics

Background:

• Coherent lattice motion driven by THz pulses offers dynamic stabilization of exotic quantum phases.
• Raman-active phonons are crucial for understanding material properties.

Purpose of the Study:

• To explore a novel mechanism for THz excitation of Raman-active phonons.
• To demonstrate THz-driven tunnel ionization as a means to excite phonons in bismuth films.

Main Methods:

• Utilized intense THz pulses (1 THz) to excite Raman-active A_{1g} phonon mode (2.9 THz) in bismuth film.
• Ruled out conventional anharmonic coupling and THz sum frequency processes.
• Investigated THz-driven tunnel ionization as the excitation mechanism.

Main Results:

• Successfully excited the Raman-active A_{1g} phonon mode in bismuth using 1 THz pulses.
• Identified THz-driven tunnel ionization as the primary mechanism for phonon excitation.
• Demonstrated a displacive driving force initiating phonon oscillations.

Conclusions:

• THz-driven tunnel ionization is a novel mechanism for exciting coherent phonons.
• This mechanism offers potential for ultrafast dynamic control of semimetals and semiconductors.
• Opens new avenues for manipulating quantum material properties.