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TT: Fachverband Tiefe Temperaturen
TT 39: Correlated Electrons: Charge Order
TT 39.5: Talk
Wednesday, March 20, 2024, 10:30–10:45, H 3025
Quenched exciton condensate in TiSe2 probed by surface-sensitive electron diffraction — •Felix Kurtz1, Tim Niklas Dauwe1, Sergey V. Yalunin1, Gero Storeck1, Jan Gerrit Horstmann2, Hannes Böckmann1, and Claus Ropers1,3 — 1Max Planck Institute for Multidisciplinary Sciences, D-37077 Göttingen — 2Department of Materials, ETH Zurich, CH-8093 Zürich — 34th Physical Institute, University of Göttingen, D-37077 Göttingen
Charge-density waves (CDWs) are intriguing correlated phenomena, arising from strong couplings among electrons or between electronic and lattice degrees of freedom. In particular, TiSe2 showcases signs of both excitonic condensation and a Peierls mechanism driving the phase transition to the CDW state below 200 K. Jointly occurring in equilibrium, time-resolved studies are capable of disentangling these contributions [1]. Here, we employ ultrafast low-energy electron diffraction (ULEED) [2] to trace the structural order parameter in the surface layer of TiSe2 after photoexcitation. We identify a low fluence threshold similar to other time-resolved works, which allows us to directly quantify the excitonic contribution to the total lattice distortion [3]. It is completely quenched at the threshold, and from the persisting distortion we estimate a 30:70 split of the structural order parameter into excitonic and Peierls contributions. Our findings highlight the strengths of ultrafast structural probing with monolayer sensitivity offered by ULEED.
[1] M. Porer et al., Nat. Mater. 13 (2014) 857.
[2] G. Storeck et al., Struct. Dyn. 7 (2020) 034304
[3] F. Kurtz et al., under review (2023)
Keywords: TMDC; Excitonic insulator; Ultrafast electron diffraction; Structural phase transition; Titanium diselenide