Berlin 2024 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 30: Ultrafast Phenomena II

HL 30.8: Talk

Wednesday, March 20, 2024, 12:00–12:15, EW 015

First-Order Rhombohedral to Cubic Phase Transition in Photoexcited GeTe — •Matteo Furci, Giovanni Marini, and Matteo Calandra — Department of Physics, University of Trento, Via Sommarive 14, 38123 Povo, Italy

Photoexcited GeTe undergoes a non-thermal phase transition from a rhombohedral to a rocksalt crystalline phase. The microscopic mechanism and the nature of the transition are unclear. By using constrained density functional perturbation theory and by accounting for quantum anharmonicity within the stochastic self-consistent harmonic approximation, we show that the non-thermal phase transition is strongly first order and does not involve phonon softening, at odd with the thermal one. The transition is driven by the closure of the single particle gap in the photoexcited rhombohedral phase. Finally, our work shows how ultrafast XRD data are consistent with a coexistence of the two phases, as expected in a first order transition. Our results are relevant for the understanding of phase transitions and bonding in phase change materials.

Keywords: Phase-Change Materials; Ultrafast Phase Transition; Structural Properties; Anharmonicity; Ferroelectricity