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Inhibition of the photoinduced structural phase transition in the excitonic insulator ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$

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

In: Physical Review B, 2018, vol. 97, no. 11, p. 115154

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...

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Ultrafast electronic band gap control in an excitonic insulator

Mor, Selene ; Herzog, Marc ; Golež, Denis ; Werner, Philipp ; Eckstein, Martin ; Katayama, Naoyuki ; Nohara, Minoru ; Takagi, Hide ; Mizokawa, Takashi ; Monney, Claude ; Stähler, Julia

In: Physical Review Letters, 2017, vol. 119, no. 8, p. 086401

We report on the nonequilibrium dynamics of the electronic structure of the layered semiconductor Ta2NiSe5 investigated by time- and angle-resolved photoelectron spectroscopy. We show that below the critical excitation density of FC=0.2 mJ cm−2, the band gap narrows transiently, while it is enhanced above FC. Hartree-Fock calculations reveal that this effect can be explained by the presence...

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