Strong Coupling of Coherent Phonons to Excitons in Semiconducting Monolayer MoTe 2 .

The coupling of the electron system to lattice vibrations and their time-dependent control and detection provide unique insight into the nonequilibrium physics of semiconductors. Here, we investigate the ultrafast transient response of semiconducting monolayer 2 H -MoTe 2 encapsulated with h BN using broadband optical pump-probe microscopy. The sub-40 fs pump pulse triggers extremely intense and long-lived coherent oscillations in the spectral region of the A' and B' exciton resonances, up to ∼20% of the maximum transient signal, due to the displacive excitation of the out-of-plane A 1g phonon. Ab initio calculations reveal a dramatic rearrangement of the optical absorption of monolayer MoTe 2 induced by an out-of-plane stretching and compression of the crystal lattice, consistent with an A 1g -type oscillation. Our results highlight the extreme sensitivity of the optical properties of monolayer TMDs to small structural modifications and their manipulation with light.