TY  - JOUR
A1  - Mor, Selene
A1  - Herzog, Marc
A1  - Noack, Johannes
A1  - Katayama, Naoyuki
A1  - Nohara, Minoru
A1  - Takagi, Hide
A1  - Trunschke, Annette
A1  - Mizokawa, Takashi
A1  - Monney, Claude
A1  - Stähler, Julia
T1  - Inhibition of the photoinduced structural phase transition in the excitonic insulator Ta2NiSe5
JF  - Physical review : B, Condensed matter and materials physics
N2  - 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 Gamma point of the Brillouin zone. The optical response saturates at a critical excitation fluence F-C = 0.30 +/- 0.08 mJ/cm(2) 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.
Y1  - 2018
U6  - https://doi.org/10.1103/PhysRevB.97.115154
SN  - 2469-9950
SN  - 2469-9969
VL  - 97
IS  - 11
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Mor, Selene
A1  - Herzog, Marc
A1  - Golez, Denis
A1  - Werner, Philipp
A1  - Eckstein, Martin
A1  - Katayama, Naoyuki
A1  - Nohara, Minoru
A1  - Takagi, Hide
A1  - Mizokawa, Takashi
A1  - Monney, Claude
A1  - Staehler, Julia
T1  - Ultrafast Electronic Band Gap Control in an Excitonic Insulator
JF  - Physical review letters
N2  - 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 F-C = 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 of the low-temperature excitonic insulator phase of Ta2NiSe5, whose order parameter is connected to the gap size. This work demonstrates the ability to manipulate the band gap of Ta2NiSe5 with light on the femtosecond time scale.
Y1  - 2017
U6  - https://doi.org/10.1103/PhysRevLett.119.086401
SN  - 0031-9007
SN  - 1079-7114
VL  - 119
SP  - 11559
EP  - 11567
PB  - American Physical Society
CY  - College Park
ER  -