Condensed Matter Seminar: Probing Crystal Symmetry and Ultrafast Dynamics in (SnS)_1.15 (TaS₂) Misfit Heterostructures

This survey investigates the structural symmetry and lattice dynamics of the (SnS)₁.₁₅(TaS₂) misfit heterostructure, a unique crystal combining semiconducting SnS and metallic TaS₂ layers.

Using Second Harmonic Generation (SHG), we identified a structural transition from a non-centrosymmetric to a centrosymmetric phase at 623 K . A key finding is that this transition occurs ~60 K lower than ferroelectric transition in isolated few-layer SnS, revealing that interlayer coupling and electronic screening from the metallic TaS₂ layers significantly reduce the energy required for the structural transition.

Ultrafast pump-probe reflectivity measurements further revealed a robust 28 GHz coherent acoustic phonon that persists from 10 K to 310 K. Crucially, this oscillation is observed even when the pump wavelength is below the SnS band gap, proving the dynamics are primarily driven by energy deposition in the metallic TaS₂ layers. Together, these results demonstrate that interlayer interactions in misfit heterostructures fundamentally modify both their equilibrium structural stability and their ultrafast dynamical response.