Role of interlayer shear phonons on lattice symmetry switching in the transition metal dichalcogenide WTe2

Coherent phonon control using ultrashort pulse trains is the key to realizing structural phase transitions in solids by nonthermal pathways. By combining double-pulse excitation and time-resolved second harmonic generation techniques under high-density electronic excitation in a two-dimensional layered material, WTe₂, we demonstrate that the lattice symmetry switching from the Weyl semimetallic Td to the semimetallic 1T^' phases is independent of the amplitude of the coherent interlayer shear phonons after the arrival of the second pump pulse. This finding provides different insights into the mechanisms for symmetry switching in which electronic excitation-driven shear sliding plays a dominant role.