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O: Fachverband Oberflächenphysik

O 40: Surface Dynamics

O 40.2: Vortrag

Dienstag, 18. März 2025, 14:15–14:30, H6

Coherent modulation of the charge density wave gap in 1T-TiSe₂ probed by tr-ARPES — •Jan Böhnke, Stephan Schmutzler, Mehul Jotshi, Cornelius Gahl, and Martin Weinelt — Freie Universität Berlin, Fachbereich Physik, Germany

Tuning the charge density wave (CDW) gap in 1T-TiSe₂ allows for the de/stabilization of the phase transition. An optical excitation breaks long-range order of the CDW state and results in a semi-metallic state on an ultrafast timescale as free carriers near the Fermi-level enhance Coulomb screening [1,2]. By employing time-resolved ARPES with 1.55 eV pump and 6.2 eV probe pulses, we discover for the first time fluence-dependent coherent modulations of the charge-density wave gap (closing and opening) in 1T-TiSe₂ at the Brillouin zone center. While for low excitation fluences, we mainly observe signatures of the CDW connected A_1g^* mode (3.45 THz), the optical A_1g phonon mode (6.1 THz) modulates the electronic structure near the gap for the high fluence regime. For an intermediate fluence we detect the transition from the A_1g^* to the A_1g mode. As we additionally find three image-potential states on the surface of 1T-TiSe₂, we can confirm the samples’ low defect density at the surface after in-vacuum cleavage.

[1] T. Rohwer et al., Nature 471, 490–493 (2011)

[2] M. Huber et al., Sci. Adv. 10, eadl4481(2024)

Keywords: TiSe2; Charge density wave; ARPES; Oscillations; Electron-phonon coupling