$T_d$ phase type-II Weyl semimetals are of technological interest in part due to their novel sliding ferroelectricity and nontrivial topology being dependent on their van der Waals stacking orders. Optical manipulation of these stacking orders via interlayer sliding can lead to new types of energy-efficient ultrafast memory and topological switches. Despite the existing reports on $T_d$ phase $\mathrm{WT}{\mathrm{e}}_2$ and $\mathrm{MoT}{\mathrm{e}}_2$, such light-driven sliding dynamics are unexplored in ternary $\mathrm{TaIr}{\mathrm{Te}}_4$, a material that has recently demonstrated more pronounced topological properties and greater environmental stability. Here we apply an ultrafast near-infrared pulse to bulk $\mathrm{TaIr}{\mathrm{Te}}_4$ and observe a $15\text{−}\mathrm{c}{\mathrm{m}}^{-1}$ coherent interlayer shear phonon in both transient reflectivity and time-resolved second harmonic generation (TRSHG). The initial cosinelike phase of this oscillation is characteristic of a displacive excitation mechanism, evidencing a pump-induced excited state distortion along the interlayer sliding coordinate. With increasing pump fluence, the temporal phase of the oscillation undergoes a π phase shift. We exclude a sliding ferroelectric switching origin using phase-sensitive TRSHG, instead concluding that the coherent phonon phase shift arises from inversion of the sliding distortion direction, supported by first-principles calculations of the crystal polarization. Our findings advance the understanding of nonequilibrium properties in layered topological semimetals and may serve as proof of principle for ultrafast electronics based on terahertz-speed modulation of the symmetry-dependent topological properties of $\mathrm{TaIr}{\mathrm{Te}}_4$.

Close

PrevNext

View figure in article

• Phonons
• Topological materials
• Transition metal dichalcogenides
• First-principles calculations
• Time-resolved reflection spectroscopy