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O: Fachverband Oberflächenphysik

O 36: Poster: Ultrafast Electron Dynamics at Surfaces and Interfaces

O 36.15: Poster

Dienstag, 19. März 2024, 18:00–20:00, Poster C

Coherent oscillations in the 4p_x,y valence band of 1T-TiSe₂ — •Jan Böhnke, Mehul Jotshi, Stephan Schmutzler, Cornelius Gahl, and Martin Weinelt — Fachbereich Physik, Freie Universität Berlin, Germany

Upon cooling below T ∼ 200 K, 1T-TiSe₂ undergoes a structural phase transition which is characterized by a charge redistribution and a periodic lattice distortion. By time-resolved ARPES it is possible to investigate the dynamics of both, electronic band structure and phonon response. Upon excitation with a fs laser pulse with 1.55 eV photon energy we observe fluence-dependent coherent oscillations in the Se 4p_x,y valence band of TiSe₂ which have been previously reported in a time-resolved photoemission experiment [1]. In contrast, no signature of coherent oscillations is found in the backfolded Ti 3d conduction band, suggesting that it is not a sensitive probe for the phase transition. Interestingly, we find image-potential states (n = 1, 2, 3) with lifetimes of up to 300 fs, indicating a low defect density of the surface after in-vacuum cleavage.

[1] S. Duan et al., Nature 595, 239-244 (2021)

Keywords: 1T-TiSe2; ARPES; Coherent oscillations; Charge-density wave; Ultrafast