The symmetry breaking induced by the ferroelectric transition often triggers the emergence of topological electronic states such as Weyl fermions in polar metals/semimetals. Such strong coupling between the lattice deformation and electronic states is therefore essentially important for the control of versatile topological phases. Here, we study the terahertz lattice and charge dynamics in ferroelectric semiconductor Sn_xPb_1-xTe thin films hosting versatile topological phases by means of the terahertz time-domain spectroscopy. With lowering the temperature, the resonant frequency of transverse optical (TO) phonon shows the significant softening and upturn. This temperature anomaly of lattice dynamics directly indicates the displacive-type ferroelectric transition. The resulting phase diagram suggests the enhancement of ferroelectricity in the films possibly due to compressive strain compared with the bulk crystals. The low-energy TO phonon induces the large DC and terahertz dielectric constant even in metallic state. Furthermore, we find that the Born effective charge of phonon mode is enhanced at around the compositions showing the band gap closing associated with the topological transition.

由铁电跃迁引起的对称性破坏通常会引发拓扑电子态的出现，例如极性金属/半金属中的外尔费米子。因此，晶格变形和电子态之间的这种强耦合对于控制通用拓扑相至关重要。在这里，我们研究了铁电半导体 Sn _x Pb _{1- x中的太赫兹晶格和电荷动力学}Te 薄膜通过太赫兹时域光谱来承载多种拓扑相。随着温度的降低，横向光学（TO）声子的共振频率呈现出明显的软化和上升趋势。这种晶格动力学的温度异常直接表明了位移型铁电转变。由此产生的相图表明，与块状晶体相比，薄膜中的铁电性增强可能是由于压缩应变。即使在金属状态下，低能 TO 声子也会引起大的 DC 和太赫兹介电常数。此外，我们发现声子模式的玻恩有效电荷在显示与拓扑跃迁相关的带隙闭合的成分周围增强。