Coherent Phonons in van der Waals MoSe₂/WSe₂ Heterobilayers

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Two-dimensional (2D) van der Waals (vdW) heterobilayers are crucial for next-generation electronic devices.
• Ultrafast control of physical properties in these 2D nanolayers is essential for advanced applications.
• Photoexcited charge carriers in vdW heterobilayers exhibit ultrafast separation, creating Coulombic forces.

Purpose of the Study:

• To investigate the generation and properties of coherent phonon modes in MoSe2/WSe2 heterobilayers.
• To explore the influence of stacking angle on phonon dynamics and photogenerated electric fields.
• To establish a novel method for THz radiation generation using modulated vdW gaps.

Main Methods:

• Utilized femtosecond laser pulses to excite MoSe2/WSe2 heterobilayers.
• Generated and detected a 0.8 THz coherent breathing mode.
• Analyzed the dependence of phonon amplitude on the stacking angle between MoSe2 and WSe2 monolayers.

Main Results:

• Successfully generated a 0.8 THz coherent breathing mode in MoSe2/WSe2 heterobilayers.
• Observed that phonon frequency and decay time are independent of stacking angle.
• Found that phonon amplitude decreases at intermediate stacking angles due to reduced photogenerated electric fields.

Conclusions:

• Coherent phonon modulation of the vdW gap in 2D heterobilayers is achievable.
• This modulation provides a new pathway for generating THz radiation.
• The findings pave the way for novel THz emitters based on vdW heterostructures.