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O: Fachverband Oberflächenphysik

O 40: Surface Dynamics

O 40.3: Vortrag

Dienstag, 18. März 2025, 14:30–14:45, H6

Impact of Coherent Phonons on Time-Resolved Optical Properties of WTe₂ — •Francesco Sammartino¹, Manuel Tuniz¹, Wibke Bronsch², Fulvio Parmigiani^1,2, and Federico Cilento² — ¹Università degli Studi di Trieste — ²Elettra - Sinctrotrone Trieste

We study the ultrafast dynamics of tungsten ditelluride (WTe₂) along both its in-plane axes, by time-resolved reflectivity (TR-R) and time-resolved second-harmonic generation (TR-SHG) experiments with a varying pump fluence.

We identify two phonon modes: the shear phonon mode at 0.24 THz, indicative of uniform in-plane atomic shifts and detected in both TR-R and TR-SHG signals, and one at 2.4 THz, detected solely in the TR-R signal. We observe a large, fluence-dependent shift of up to ≈90^∘ in the initial phase of the shear mode coherent oscillation, obtained in a narrow fluence range.

This evidence suggests that the excitation density can be used as a powerful knob to control the initial phase of the atomic displacements in a layered material.

Keywords: Coherent phonons; Ultrafast dynamics (pump-probe experiment); Transition metal dichalcogenides; Time Resolved Reflectivity and SHG; Non-centrosymmetric materials