Strongly Coupled Coherent Phonons in Single-Layer MoS2

We present a transient absorption setup combining broadband detection over the visible–UV range with high temporal resolution (∼20 fs) which is ideally suited to trigger and detect vibrational coherences in different classes of materials. We generate and detect coherent phonons (CPs) in single-layer (1L)-MoS₂, as a representative semiconducting 1L-transition metal dichalcogenide (TMD), where the confined dynamical interaction between excitons and phonons is unexplored. The coherent oscillatory motion of the out-of-plane A′₁ phonons, triggered by the ultrashort laser pulses, dynamically modulates the excitonic resonances on a time scale of few tens of fs. We observe an enhancement by almost 2 orders of magnitude of the CP amplitude when detected in resonance with the C exciton peak, combined with a resonant enhancement of CP generation efficiency. Ab initio calculations of the change in the 1L-MoS₂ band structure induced by the A′₁ phonon displacement confirm a strong coupling with the C exciton. The resonant behavior of the CP amplitude follows the same spectral profile of the calculated Raman susceptibility tensor. These results explain the CP generation process in 1L-TMDs and demonstrate that CP excitation in 1L-MoS₂ can be described as a Raman-like scattering process.

C.Trovatello, H.P.C. Miranda, A. Molina-Sánchez, R. Borrego-Varillas, C. Manzoni, L. Moretti, L. Ganzer, M. Maiuri, J. Wang, D. Dumcenco, A. Kis, L. Wirtz, A. Marini, G. Soavi, A.C. Ferrari, G. Cerullo, D. Sangalli, and S. Dal Conte. Strongly Coupled Coherent Phonons in Single-Layer MoS₂. ACS Nano 14, 5 (2020)

We present a transient absorption setup combining broadband detection over the visible–UV range with high temporal resolution (∼20 fs) which is ideally suited to trigger and detect vibrational coherences in different classes of materials. We generate and detect coherent phonons (CPs) in single-layer (1L)-MoS2, as a representative semiconducting 1L- https://pubs.acs.org/doi/full/10.1021/acsnano.0c00309