Efficient launching of shear phonons in photostrictive halide perovskites.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 41191747.
- Also identified by DOI 10.1126/sciadv.adw9172 and PMC identifier 13141899.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
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<sub>2</sub>AgBiBr<sub>6</sub>, 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<sub>2</sub>AgBiBr<sub>6</sub> 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 <i>c</i> 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.