This thesis presents an experimental study of the static and ultrafast electronic structure of the ferroelectric IV–VI semiconductors SnTe and GeTe. Using angle‑resolved photoemission spectroscopy (ARPES), we investigated the evolution of electronic bands across the ferroelectric transition, revealing a persistent Rashba‑type splitting above the critical temperature, that serves as evidence for local structural distortions and an order–disorder character of the transition. Time‑resolved ARPES measurements further uncovered out‑of‑equilibrium mechanisms enabling a transient coexistence of ferroelectricity and topological character through Floquet engineering. In GeTe(111), we additionally identified image‑potential states with unexpectedly large spatial extension above the vacuum level, alongside characteristic relaxation pathways of photoexcited carriers.

While the thesis encompasses the broader study of ferroelectric transitions, equilibrium and non‑equilibrium band structures, and the discovery of image‑potential states, the presentation will concentrate exclusively on the emergence of Floquet topological states in SnTe.
The talk will begin with a pedagogical introduction to guide a general audience through the concepts underlying this phenomenon.