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Strongly Coupled Coherent Phonons in Single-Layer MoS2.
Chiara Trovatello1, Henrique P C Miranda2, Alejandro Molina-Sánchez3
1Dipartimento di Fisica, Politecnico di Milano, Piazza L. da Vinci 32, I-20133 Milano, Italy.
ACS Nano
|April 3, 2020
Summary
We developed a new setup to study vibrational coherences in materials. This system successfully generated and detected coherent phonons in single-layer molybdenum disulfide (MoS2), revealing strong exciton-phonon coupling.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Spectroscopy
Background:
- Understanding exciton-phonon interactions is crucial for exploring dynamical processes in low-dimensional materials.
- Single-layer transition metal dichalcogenides (TMDs) exhibit unique optoelectronic properties influenced by coupled electron-lattice dynamics.
- Previous studies have not fully explored the interplay between excitons and coherent phonons in semiconducting 1L-TMDs.
Purpose of the Study:
- To investigate the generation and detection of coherent phonons (CPs) in single-layer molybdenum disulfide (1L-MoS2).
- To explore the dynamical interaction between excitons and phonons in 1L-MoS2 using a high-temporal-resolution transient absorption setup.
- To elucidate the mechanism of CP generation and its resonant enhancement in 1L-TMDs.
Main Methods:
- Development of a transient absorption setup with broadband visible-UV detection and femtosecond temporal resolution (∼20 fs).
- Generation and detection of coherent phonons (CPs) in single-layer MoS2 triggered by ultrashort laser pulses.
- Utilizing ab initio calculations to study the band structure changes induced by A'1 phonon displacement and comparing with experimental Raman susceptibility.
Main Results:
- Observed coherent oscillatory motion of out-of-plane A'1 phonons modulating excitonic resonances on a tens-of-femtoseconds timescale.
- Demonstrated a significant enhancement (nearly 2 orders of magnitude) of the CP amplitude when detected in resonance with the C exciton peak.
- Confirmed resonant enhancement of CP generation efficiency and strong coupling between the C exciton and A'1 phonon displacement via calculations.
Conclusions:
- The study explains the CP generation process in 1L-TMDs, highlighting the significant role of exciton-phonon coupling.
- CP excitation in 1L-MoS2 can be effectively described as a Raman-like scattering process.
- The developed transient absorption setup is well-suited for probing vibrational coherences and exciton-phonon dynamics in various materials.
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