研究目的
To understand the mechanism underlying the coherent phonon (CP) generation process and to identify the physical parameters (such as the pump pulse photon energy) that allow their efficient excitation in single-layer MoS2.
研究成果
The study demonstrated that A'1 optical phonon modes strongly couple with the C exciton, giving rise to a temporal modulation of the TA response over a broad energy range around this excitonic peak. The excitation profile of such coherent oscillations follows the energy dependence of the Raman tensor, proving that the lattice coherence in 1L-MoS2 can be described as a Raman-like excitation mechanism. Ab Initio calculations of the band structure for displaced atoms configuration confirm the strong coupling between C exciton and A'1 phonons.
研究不足
The study was restricted to a narrow energy range (～100meV) around the A exciton, making it difficult to gain information on how CP excitation affects the whole band structure. The phonon dephasing time τdeph=1.7±0.2ps is almost three times smaller than that measured at the same temperature for CP in exfoliated 1L-WSe2, possibly due to different defect concentration in exfoliated and CVD-grown 1L-TMDs.
1：Experimental Design and Method Selection:
A transient absorption setup combining broadband detection from 1.8 to 3eV with extremely high temporal resolution (～20fs) was used to trigger and detect vibrational coherences in single-layer MoS
2：8 to 3eV with extremely high temporal resolution (～20fs) was used to trigger and detect vibrational coherences in single-layer MoSSample Selection and Data Sources:
2.
2. Sample Selection and Data Sources: Large area (i.e. mm sized) chemical vapor deposition (CVD) 1L-TMDs were used due to the minimum spot size of the pump and probe pulses in the high temporal resolution setup being larger than the typical size of mechanically exfoliated 1L-TMDs.
3：List of Experimental Equipment and Materials:
The setup included a frequency-tunable ultrashort pulses<20fs, a white-light supercontinuum probe pulse, and a Si spectrometer working at the full laser repetition rate.
4：Experimental Procedures and Operational Workflow:
The sample was photo-excited with frequency-tunable ultrashort pulses, and the differential transmission (?T /T ) was measured by a white-light supercontinuum probe pulse whose spectral content covers all excitonic resonances.
5：Data Analysis Methods:
The frequency of the residual oscillations was determined by performing a Fourier Transform (FT) analysis.
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