Phonon Dephasing Dynamics in MoS₂.

Area of Science:

• Quantum information science
• Condensed matter physics
• Materials science

Background:

• Atomically thin van der Waals materials offer quantum degrees of freedom for quantum information applications.
• These quantum properties interact with phonons, influencing their coherence.
• Understanding phonon decoherence is crucial for developing robust quantum technologies.

Purpose of the Study:

• To directly measure the intrinsic optical phonon decoherence in monolayer and bulk molybdenum disulfide (MoS₂).
• To investigate the temperature dependence of phonon dephasing times.
• To elucidate the mechanisms underlying optical phonon decay.

Main Methods:

• Utilized time-resolved spectral interference of Stokes photons generated by pulsed lasers.
• Measured the temporal evolution of phonon-induced spectral changes.
• Performed first-principles calculations to model phonon decay processes.

Main Results:

• The prominent E_2g optical phonon mode in MoS₂ exhibits a room-temperature dephasing time of approximately 7 picoseconds (ps) for both monolayer and bulk.
• At low temperatures (~15 K), the dephasing time in bulk MoS₂ extends to approximately 20 ps.
• First-principles calculations indicate that optical phonons decay through three-phonon processes, generating pairs of acoustic phonons.

Conclusions:

• The measured phonon dephasing times provide critical insights into the coherence properties of MoS₂.
• The extended dephasing times at low temperatures suggest potential for improved quantum information processing.
• The identified three-phonon decay mechanism is key to understanding phonon dynamics in MoS₂.