Ultrafast Polarization-Resolved Phonon Dynamics in Monolayer Semiconductors

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Optics

Background:

• Monolayer transition metal dichalcogenides (TMDs) possess unique valleytronic properties.
• These properties arise from interactions with chiral phonons, which break time-reversal symmetry.

Purpose of the Study:

• To investigate the ultrafast dynamics of phonons in monolayer WS2.
• To understand the role of phonon coherence and decoherence in 2D materials.

Main Methods:

• Excitation using intense, resonant, and polarization-tunable terahertz pulses.
• Probing phonon dynamics via time-resolved anti-Stokes Raman spectroscopy.
• Separation of coherent and incoherent phonon populations.

Main Results:

• Observed ultrafast dynamics of linearly and circularly polarized E'(Γ) phonons.
• Incoherent phonon population lifetime exceeds coherence lifetime, indicating significant decoherence.
• Faster depolarization in circular bases points to linearly polarized eigenstates due to lattice anisotropy.

Conclusions:

• Inhomogeneous broadening and momentum scattering are crucial for phonon decoherence at room temperature.
• Lattice anisotropy influences phonon polarization dynamics in 2D materials.
• Findings offer insights for enhancing chiral phonon lifetimes and controlling spin-orbital polarization in quantum materials.