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arXiv · 1804.00882

Inhibition of the photoinduced structural phase transition in the excitonic insulator Ta$_2$NiSe$_5$

Selene Mor·Marc Herzog·Johannes Noack·Naoyuki Katayama·Minoru Nohara·Hide Takagi·Annette Trunschke·Takashi Mizokawa·Claude Monney·Julia Stähler
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Abstract

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.

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Selene Mor, Marc Herzog, Johannes Noack, Naoyuki Katayama, Minoru Nohara, Hide Takagi, Annette Trunschke, Takashi Mizokawa, Claude Monney, Julia Stähler. 2018-04-03. Inhibition of the photoinduced structural phase transition in the excitonic insulator Ta$_2$NiSe$_5$. https://doi.org/10.1103/physrevb.97.115154

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