Year: 2025
Type: article
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 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.
Source: Science Advances
Institutions: TU Dortmund University, Technische Universität Berlin, Centre National de la Recherche Scientifique, Le Mans Université, Laboratoire d'Acoustique de l'Université du Mans, University of Würzburg, Complexity, Topology and Dynamics in Quantum Matter, Research Center Future Energy Materials and Systems
Language: English
Subfield: Electrical and Electronic Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,500
OpenAlex ID: W4415992348