Floquet topological insulator in out-of-equilibrium α-SnTe

α-SnTe offers a combination of semiconducting and polar properties, further enriched by a non-trivial topological behavior. At low temperature, a structural distortion breaks inversion symmetry and leads to a macroscopic electric polarization, resulting in a significant Rashba splitting in the valence band. In the first part of my talk, I present how, by using photoemission spectroscopy, we track the evolution of the Rashba splitting as an indicator of the distortion to provide insights into the polar structural transition, suggesting an order-disorder phase transition with substantial deviations from a mean-field-like behavior.

Moving to the second part, I focus on the topological properties of SnTe. While it has been theoretically predicted that a metallic topological surface state is present in an undistorted structure, the break of mirror symmetry in the polar structure suppresses it. However, I show how we can use a photoexcitation in this distorted case to produce a topological state. By employing ultrashort and tailored light pulses, we create a Floquet replica of the valence band that interacts with the conduction band. A careful fluence and wavelength dependent study allows us to investigate the concomitant conditions to generate an ultrashort light-induced and unexpected topological state, even while the atomic structure remains distorted.