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Direct View of Phonon Dynamics in Atomically Thin MoS2.
Tristan L Britt1, Qiuyang Li2, Laurent P René de Cotret1
1Department of Physics, Center for the Physics of Materials, McGill University, 3600 rue Université, Montréal, Québec H3A 2T8, Canada.
Nano Letters
|June 7, 2022
Summary
This study quantifies electron-phonon coupling and heat transport in 2D materials. Ultrafast electron diffraction reveals anisotropic phonon behavior and highlights the role of dielectric screening in weakening electron-phonon coupling.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Nanotechnology
Background:
- Two-dimensional (2D) materials like transition-metal dichalcogenide monolayers offer tunable properties for fundamental physics studies.
- While electron behavior is well-studied, the role of phonons (lattice vibrations) in 2D systems is crucial but less understood.
- Electron-phonon coupling (EPC) significantly influences material properties and thermal transport.
Purpose of the Study:
- To directly quantify electron-phonon coupling (EPC) in monolayer molybdenum disulfide.
- To investigate phonon transport from a 2D material to a substrate.
- To understand the influence of dielectric screening on EPC dynamics in the 2D limit.
Main Methods:
- Utilized ultrafast electron diffraction and diffuse scattering for time and momentum-resolved measurements.
- Employed optical excitation to generate hot carriers and initiate dynamics.
- Performed ab initio ultrafast dynamics simulations for quantitative comparison.
Main Results:
- Observed a highly anisotropic phonon distribution in the monolayer within picoseconds after optical excitation.
- Demonstrated that dielectric screening significantly weakens EPC in the 2D material.
- Found that thermal transport to the substrate occurs under non-equilibrium phonon conditions.
Conclusions:
- Dielectric screening plays a critical role in weakening EPC, extending beyond equilibrium properties to dynamic regimes.
- Phonon transport in 2D materials is complex and occurs far from thermal equilibrium.
- This work provides new insights into the fundamental dynamics of heat and energy transfer in 2D materials.
