Dresden 2020 – wissenschaftliches Programm
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O 44.2: Vortrag
Dienstag, 17. März 2020, 11:00–11:15, WIL B321
Atomically resolved femtosecond pump probe measurements on Ta2NiSe5 — •Lukas Arnhold1, Gregory McMurtrie1, Shaoxiang Sheng1, Mohamad Abdo1,2, and Sebastian Loth1,2 — 1University of Stuttgart, Institute for Functional Matter and Quantum Technologies, Stuttgart, Germany — 2Max Planck Institute for Solid State Research, Stuttgart, Germany
The investigation of new and interesting phases in solids is one of the major goals of condensed matter physics. Ta2NiSe5, a putative excitonic insulator, is a material in which the exciton binding energy can exceed the band gap energy, leading to spontaneous condensation of excitons  following Bose-Einstein-statistics.
In such a material, it would be particularly interesting to locally break individual excitons and observe the re-condensation into the ground state.
To this end, we combine scanning tunneling microscopy (STM) with ultrafast THz light pulses. This boosts the STM's time resolution to the femtosecond range  making it possible to observe the fast electronic dynamics of correlated ground states in real space.
In static measurements, as we decrease the tunnel resistance, we observe a closing of the excitonic band gap. This closing coincides with an unusual increase of THz current in pump probe measurements. We study the dynamic response with atomic spatial resolution in particular around atomic defects in the surface layer.
 Lu, Y. et al., Nat Commun 8, 14408 (2017)  Cocker, T. et al., Nature Photon 7, 620*625 (2013)