Efficient launching of shear phonons in photostrictive halide perovskites
- Dmytro O. Horiachyi
- Mikhail O. Nestoklon
- Ilya A. Akimov
- Artur V. Trifonov
- Nikita V. Siverin
- Nataliia E. Kopteva
- Alexander N. Kosarev
- Dmitri R. Yakovlev
- Vitalyi E. Gusev
- Melina Fries
- Olga Trukhina
- Vladimir Dyakonov
- Manfred Bayer
2025-11-05
Optical generation of coherent transverse phonons by femtosecond light pulses is appealing for sub-terahertz high-speed active control of material properties. Lead-free double-perovskite semiconductors, such as Cs 2 AgBiBr 6 , attract particular interest in this respect due to their structural phase transition and strong carrier-lattice coupling. Here, we reveal that the giant anisotropic photostriction in halide perovskites with tetragonal crystal structure provides an efficient nonthermal tool for generating coherent transverse phonons. Using time-domain Brillouin spectroscopy, we observe transverse and longitudinal acoustic phonons with comparable amplitudes in the tetragonal phase of Cs 2 AgBiBr 6 below the temperature of 122 kelvins, while, in the cubic phase, only longitudinal phonons are generated. The polarization of the transverse phonons is dictated by the projection of the crystal c axis on the surface plane, which leads to a prominent anisotropic polarization response in the detection. The generated strain pulses correspond to soft transverse acoustic eigenmodes with a strong temperature dependence of dispersion, providing an additional degree of freedom for hypersonic manipulation.