Mor, Selene Herzog, Marc Noack, Johannes Katayama, Naoyuki Nohara, Minoru Takagi, Hide Trunschke, Annette Mizokawa, Takashi Monney, Claude Stähler, Julia 2018-03-26 Femtosecond time-resolved midinfrared reflectivity is used to investigate the electron and phonon dynamics occurring at the direct band gap of the excitonic insulator Ta2NiSe5 below the critical temperature of its structural phase transition. We find that the phonon dynamics show a strong coupling to the excitation of free carriers at the Γ point of the Brillouin zone. The optical response saturates at a critical excitation fluence FC=0.30±0.08 mJ/cm2 due to optical absorption saturation. This limits the optical excitation density in Ta2NiSe5 so that the system cannot be pumped sufficiently strongly to undergo the structural change to the high-temperature phase. We thereby demonstrate that Ta2NiSe5 exhibits a blocking mechanism when pumped in the near-infrared regime, preventing a nonthermal structural phase transition. application/pdf https://folia.unifr.ch/global/documents/306677 https://folia.unifr.ch/documents/306677/files/mon_ips.pdf eng info:eu-repo/semantics/altIdentifier/doi/10.1103/PhysRevB.97.115154 info:eu-repo/semantics/openAccess License undefined Physical Review B. - 2018, vol. 97, no. 11, p. 115154 info:eu-repo/classification/udc/53 Inhibition of the photoinduced structural phase transition in the excitonic insulator ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$ http://purl.org/coar/resource_type/c_6501