Photoinduced Interlayer Dynamics in T${}_d$-MoTe${}_2$: A Broadband Pump-Probe Study

We report on time-resolved broadband transient reflectivity (tr-bb-TR) measurements performed on a bulk single crystal of T${}_d$-MoTe${}_2$ as a function of the incident pump fluence (F). Tr-bb-TR data unveil photoinduced electronic changes progressing on the sub-picosecond timescale as well as the dynamics of the coherent low-frequency ${}^1{A}_1$ interlayer shear phonon. Our results indicate a gradual evolution of both the TR and the ${}^1{A}_1$ Fourier intensity spectra as a function of F, ruling out the threshold-like change that has been associated with the ultrafast photoinduced $T_d\to 1T^{\mathrm{\prime }}$ phase transition. We also observe a large redshift of the ${}^1{A}_1$ Fourier spectral features, which suggests that large renormalization effects are taking place on interband transitions that are dielectrically susceptible to the ${}^1{A}_1$ interlayer phonon displacement.