Regensburg 2025 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 2: 2D Semiconductors and van der Waals Heterostructures I

HL 2.10: Talk

Monday, March 17, 2025, 12:00–12:15, H15

Ultrafast pump-probe spectroscopy of WSe2 multilayer bubbles — •Jens-Christian Drawer, Henri Melchert, Marti Struve, Christian Schneider, and Martin Esmann — Carl von Ossietzky Universität Oldenburg, Oldenburg, Germany

Heterostructures of van der Waals materials have recently emerged as a versatile platform for the tailored generation and detection of coherent acoustic phonons in the GHz up to THz frequency range [1]. In this work, we investigate WSe2 layers of different thicknesses by ultrafast pump-probe spectroscopy and observe thickness-dependent breathing-type acoustic phonon modes up to 850 GHz in frequency in the bilayer case. Under suitably chosen conditions for the dry-gel stamping preparation, 40 nm thick WSe2 flakes form nanobubbles. For these bubbles, our pump-probe measurements reveal a significant improvement in the quality factor of their fundamental 29 GHz acoustic Fabry-Pérot mode from Q=13.9±0.7 to Q=141±5. We then tailor these high-Q modes by encapsulating the bubbles with hBN, introducing new spectral features attributed to coupled acoustic modes between WSe2 and hBN. For example, our approach may enable the ultrafast modulation of strain-defined quantum emitters found in WSe2.

[1] Yoon, Y. et al.. Nature 631, 771–776 (2024).

Keywords: two-dimensional materials; pump-probe spectroscopy; acousto-optics