Inhibition of the photoinduced structural phase transition in the excitonic insulator Ta$_2$NiSe$_5$
- Resource Type
- Working Paper
- Authors
- Mor, Selene; Herzog, Marc; Noack, Johannes; Katayama, Naoyuki; Nohara, Minoru; Takagi, Hide; Trunschke, Annette; Mizokawa, Takashi; Monney, Claude; Stähler, Julia
- Source
- Subject
- Condensed Matter - Strongly Correlated Electrons
- Language
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 Ta$_2$NiSe$_5$ 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 \Gamma\ point of the Brillouin zone. The optical response saturates at a critical excitation fluence $F_C = 0.30~\pm~0.08$~mJ/cm$^2$ due to optical absorption saturation. This limits the optical excitation density in Ta$_2$NiSe$_5$ so that the system cannot be pumped sufficiently strongly to undergo the structural change to the high-temperature phase. We thereby demonstrate that Ta$_2$NiSe$_5$ exhibits a blocking mechanism when pumped in the near-infrared regime, preventing a nonthermal structural phase transition.