Berlin 2024 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 8: Ultrafast Phenomena I

HL 8.9: Talk

Monday, March 18, 2024, 17:15–17:30, EW 015

Molecular dynamics simulations of ultrafast thermodynamics in SrTi03 — •Fredrik Eriksson, Erik Fransson, Richard Matthias Geilhufe, and Paul Erhart — Departement of physics, Chalmers university of technology, Gothenburg, Sweden

The possibility to control and probe materials in the ultrafast regime has opened up several new areas in fundamental research and engineering. In this regard characterization of ultrafast time-dependent thermodynamic properties within the material is crucial [1]. Here, we analyze these aspects by molecular dynamics for the cubic perovskite SrTi03. In particular we artificially excite the ferroelectric optical phonon mode at the zone center, mimicking a laser response. The mode interactions and decay pathways are analyzed and compared to theoretical and experimental data. We find that after about 500fs of pumping the ferroelectric mode, a higher frequency optical mode at Gamma, around 6THz, is strongly excited and pushed out of its equilibrium distribution. This observation is in good agreement with recent experimental work using time-resolved X-ray scattering where this upconversion was also observed [2]. The method allows for a detailed understanding of the entropy production in the system from first principles. In addition, the microscopic mechanism responsible for the upconversion are outlined.

[1] Caprini et al. arXiv:2302.02716v2 (2022)

[2] Kozina et al. Nat. Phys. 15, 387-392 (2019)

Keywords: STO; Molecular dynamics; Ultrafast; Stochastic thermodynamics; Phonon