Berlin 2024 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 8: Ultrafast Phenomena I

HL 8.3: Talk

Monday, March 18, 2024, 15:30–15:45, EW 015

Light-Induced Nonthermal Phase Transition to the Topological Crystalline Insulator State in SnSe — •Stefano Mocatti, Giovanni Marini, and Matteo Calandra — Department of Physics, University of Trento, Via Sommarive 14, 38123 Povo, Italy

Femtosecond pulses have been used to reveal hidden broken symmetry phases and induce transitions to metastable states. However, these states are mostly transient and disappear after laser removal. Photoinduced phase transitions toward crystalline metastable states with a change of topological order are rare and difficult to predict and realize experimentally. In this presentation, by means of constrained density functional perturbation theory and non-perturbative light-induced quantum anharmonicity, we show that ultrafast lasers can permanently transform the topologically trivial orthorhombic structure of SnSe into the topological crystalline insulating rocksalt phase via a first-order nonthermal phase transition (1). We describe the reaction path and evaluate the critical fluence and possible decay channels after photoexcitation. Our simulations of the photoexcited structural and vibrational properties are in excellent agreement with recent pump-probe data in the intermediate fluence regime below the transition, with an error on the curvature of the quantum free energy of the photoexcited state that is smaller than 2%.

(1) S. Mocatti, G. Marini, M. Calandra, J. Phys. Chem. Lett. 2023, 14, 41, 9329-9334

Keywords: First-principles calculations; Ultrafast phase transition; Light-matter interaction; Quantum anharmonicity; Lattice dynamics