Nonequilibrium carrier dynamics in FeSe 0.8 Te 0.2

We report on the nonequilibrium dynamics of photoinduced collective excitations in FeSe 0.8 Te 0.2 superconducting (SC) thin film. The obtained transient reflectance traces show three distinct regions attributed to different dynamical processes. First two processes are observed within a sub-picosecond scale and are associated with photoexcitation of quasi-particles (QP). The first process is attributed to QPs accumulation and is sensitive to structural anisotropy. We use nematicity measurements to determine its time constant. The electron–phonon coupling constant of λ = 0.2 was derived and is consistent with previous studies for similar materials. Strong acoustic phonons generation was observed on a longer timescale. Graphical abstract