Regensburg 2025 – scientific programme

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O: Fachverband Oberflächenphysik

O 40: Surface Dynamics

O 40.1: Talk

Tuesday, March 18, 2025, 14:00–14:15, H6

Manipulation of Optical Phonons in Strained Bi/Si(001) Heterostructures — •Fabian Thiemann and Michael Horn-von Hoegen — University of Duisburg-Essen, Lotharstr. 1, 47057 Duisburg, Germany

Intentionally manipulating phononic properties in materials can cause dramatic changes in their dynamic behavior. A system that responds especially strong to structural changes is Bi due to its strong electron-phonon coupling and its inherent Peierls distortion. This renders the optical A_1g mode – oscillating along the [111] direction – sensitive to changes in the electronic system and coherently excitable upon photoexcitation. When grown on Si(001) bismuths lattice matches in the [110] direction, resulting in a compressive strain in the [110] direction, whereas the films are [111] oriented. The strain is relieved rapidly while increasing the thickness from 10 to 16 BL. This is predicted to influence the Peierls distortion heavily. In this work we extensively studied the impact of strain and confinement on the photoexcited coherent A_1g mode’s frequency and dephasing in Bi/Si(001) heterostructures by in-situ transient-reflectivity spectroscopy. We observe a dramatic blueshift up to 0.2 THz, that can be preciesely tuned by the film thickness. The frequency however does not follow exactly the strain parameter and behaves differently in two regiemes. We attribute this discrepancy to the confinement in the [111] direction and the influence of the strongly shifting electron surface state.

Keywords: coherent phonons; heterostructures; transient-reflectivity spectroscopy; bismuth