Launching Coherent Acoustic Phonon Wave Packets with Local Femtosecond Coulomb Forces

Area of Science:

• Solid-state physics
• Nanotechnology
• Terahertz science

Background:

• Coherent acoustic phonons are crucial for ultrafast control of solids and acoustic devices.
• Existing methods for phonon generation have limitations in precision and scale.

Purpose of the Study:

• To demonstrate a novel method for launching localized coherent acoustic phonon wave packets.
• To explore the application of ultrafast Coulomb forces for precise control of atomic-scale lattice dynamics.

Main Methods:

• Utilizing a scanning tunneling microscope (STM) with tip-enhanced terahertz electric fields.
• Employing ultrafast Coulomb forces to excite and launch phonon wave packets.
• Analyzing wave packet propagation and standing wave formation in thin gold films.

Main Results:

• Successfully launched localized coherent acoustic phonon wave packets.
• Observed wave packet propagation at longitudinal acoustic phonon speed.
• Generated standing waves up to 0.26 THz in a 6.4 nm Au film.
• Achieved ultrafast lattice displacement up to 5 pm, controllable via tip-sample distance.

Conclusions:

• Ultrafast Coulomb forces provide a nonthermal mechanism for generating coherent phonons at the atomic scale.
• This technique is applicable to nano-optomechanics and advanced terahertz engineering.
• Opens new avenues for exploiting coherent phonons in nanoscale devices.