Ultrafast dynamics of Mott-state quench and formation in strongly correlated BEDT-TTF molecular conductors observed by three-pulse pump probe spectroscopy

S. Tsuchiya,1,2 H. Taniguchi,1 J. Yamada,3 Y. Toda,2 D. Mihailovic,1,4 T. Mertelj1,4

1Complex Matter Department, Jozef Stefan Institute, Jamova 39, Ljubljana, SI-1000, Slovenia

2Department of Applied Physics, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan

3Graduate School of Material Science, University of Hyogo, Hyogo 678-1205, Japan

4Center of Excellence on Nanoscience and Nanotechnology Nanocenter (CENN Nanocenter), Jamova 39, 1000 Ljubljana, Slovenia

We investigate the quench and real-time formation of the Mott state and photoexcited carrier relaxation dynamics in the Mott insulator κ-(BEDT-TTF)2Cu[N(CN)2]Cl (κ-Cl) and the superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br (κ-Br) using three-pulse femtosecond optical spectroscopy. In both salts, we find that transient reflectivity amplitude recovers on 2 ps timescale after a strong near-infrared pulse quench. The transient reflectivity relaxation time is nearly constant throughout indicating that the energy gap for charge excitations is filled rather than closed, by photoinduced carriers of only 0.5% per dimer site. The Mott state is re-formed on a few-picosecond timescale with the disappearance of the in-gap photo-doping induced states near the Fermi energy. In κ-Br, a similar behavior to that in κ-Cl is observed and attributed to the disorder induced phase-separated Mott insulating regions [2].

1. S. Tsuchiya et al., Phys. Rev. B 104, 115152 (2021).
2. Y. Toda, et al., Phys. Rev. Lett. 107, 227002 (2011).

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