The temporal characters of laser-driven phase transition from $2H$ to $1T^{\prime }$ has been investigated in the prototype ${\mathrm{MoTe}}_2$ monolayer. This process is found to be induced by fundamental electron-phonon interactions, with an unexpected phonon excitation and coupling pathway closely related to the nonequilibrium relaxation of photoexcited electrons. The order-to-order phase transformation is dissected into three substages, involving energy and momentum scattering processes from optical ($A_1^{\prime }$ and $E^{\prime }$) to acoustic phonon modes [LA(M)] in subpicosecond timescale. An intermediate metallic state along the nonadiabatic transition pathway is also identified. These results have profound implications on nonequilibrium phase engineering strategies.

• Received 5 August 2021
• Revised 28 November 2021
• Accepted 7 December 2021

DOI:https://doi.org/10.1103/PhysRevLett.128.015702