  Time-domain femtosecond laser spectroscopic measurements of the ultrafast
lattice dynamics in 2H-MoTe2 bulk crystals were carried out to understand the
carrier-phonon interactions that govern electronic transport properties. An
unusually long lifetime coherent A1g phonon mode was observed even in the
presence of very large density of photo-excited carriers at room temperature.
The decay rate was observed to decrease with increasing excitation laser
fluence. Based on the laser fluence dependence including the inducement of
significant phonon softening and a peculiar decrease in phonon decay rate, we
attribute the long lifetime lattice dynamics to weak anharmonic phonon-phonon
coupling and a carrier-density-dependent deformation potential electron-phonon
coupling.
