Selene Mor, Marc Herzog, Johannes Noack, Naoyuki Katayama, Minoru Nohara, Hide Takagi, Annette Trunschke, Takashi Mizokawa, Claude Monney, and Julia Stähler:
Phys. Rev. B 97 (11), 115154 (2018), pp.5;
Femtosecond time-resolved mid-infrared 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 strong 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 non-thermal structural phase transition.
The original publication is available by link DOI: 10.1103/PhysRevB.97.115154