Designing Coherent Energy Flow in Group 5 Semiconductors

Coherent energy transport offers a way to overcome the resistive limitations of conventional semiconductors by allowing wave-like propagation without scattering or phase loss. Here, stroboscopic scattering microscopy (stroboSCAT) reveals coherent quasiparticle motion in three group 5 semiconductors: Nb₃Se₁₀Cl₂ (a new 1-D van der Waals chain), NbOI₂ (a 2-D ferroelectric), and V₄S₉Br₄ (a 2-D antiferromagnet). In Nb₃Se₁₀Cl₂, carriers move quasi-ballistically up to 590 km/s within 450 fs, due to the coherence promoted by the J-aggregation of Nb₃Se₈Cl₄ subunits. In NbOI₂, above gap excitation triggers long-lived, THz oscillations of its ferroelectric order that travel along the polar axis above 100 km/s. In V₄S₉Br₄, below gap excitation prompts a photothermal phase transition that drastically changes reflectance and magnetic ordering. Across all three, the local structure of the group 5 metal dictates the material response, either in the anisotropy of directional propagation, or distorsions responsible for phase transitions. This exemplifies stroboSCAT as a versatile method for identifying coherent energy flow and points to guiding principles for the directed synthesis of future excitonic and THz-active materials.