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TT: Fachverband Tiefe Temperaturen

TT 39: Correlated Electrons: Charge Order

TT 39.5: Vortrag

Mittwoch, 20. März 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 Ropers^1,3 — 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