Phonon-Assisted Intervalley Scattering Determines Ultrafast Exciton Dynamics in MoSe_{2} Bilayers.

Area of Science:

• Solid-state physics
• Quantum optics
• Materials science

Background:

• Valleys in solid band structures are energy extrema.
• Atomically thin transition metal dichalcogenides (TMDCs) exhibit unique exciton dynamics influenced by these valleys.

Purpose of the Study:

• To investigate and compare exciton decoherence timescales in MoSe2 monolayers and bilayers.
• To elucidate the microscopic mechanisms governing exciton quantum dynamics in TMDC bilayers.

Main Methods:

• Utilized two-dimensional coherent electronic spectroscopy to probe exciton dynamics.
• Developed a microscopic model to analyze phonon-emission scattering processes.

Main Results:

• Exciton decoherence occurs on a significantly faster timescale in MoSe2 bilayers compared to monolayers.
• Identified both coherent and incoherent population relaxation channels in TMDC bilayers.
• Discovered that phonon-emission processes drive scattering from the K valley to lower-energy Γ and Λ valleys in bilayers.

Conclusions:

• Established distinct microscopic mechanisms for exciton quantum dynamics in TMDC monolayers versus bilayers.
• Understanding these dynamics is crucial for controlling spin-valley degrees of freedom in TMDC bilayers.