Optically driven coherent shear phonons in lead-free double perovskites

Dmytro Horiachyi^a, Mikhail Nestoklon^a, Ilya Akimov^a, Artur Trifonov^a, Nikita Siverin^a, Nataliia Kopteva^a, Alexander Kosarev^a, Dmitri Yakovlev^a, Vitalyi Gusev^b, Melina Fries^c, Olga Trukhina^c, Vladimir Dyakonov^c, Manfred Bayer^a^,^d

^aExperimental Physics 2, TU Dortmund University, 44227 Dortmund, Germany

^bLaboratoire d’Acoustique de l’Université du Mans (LAUM), UMR CNRS 6613, Institut d’Acoustique-Graduate School (IA-GS), Le Mans Université, Le Mans, France

^cExperimental Physics 6 and Würzburg-Dresden Cluster of Excellence ct.qmat, Julius-Maximilians-Universität Würzburg, 97070 Würzburg, Germany

^dResearch Center Future Energy Materials and Systems, Technische Universität Dortmund, 44227 Dortmund, Germany

Proceedings of Perovskite Semiconductors: From Fundamental Properties to Devices (PerFunPro)

Konstanz, Germany, 2025 September 8th - 10th

Organizers: Lukas Schmidt-Mende, Vladimir Dyakonov and Selina Olthof

Poster, Ilya Akimov, 039
Publication date: 9th July 2025

Optically generated sub-THz coherent acoustic phonons exhibit significant potential for controlling and manipulating various material properties. Halide perovskite semiconductors, such as lead-free double Cs2AgBiBr6, are particularly interesting for these purposes due to cubic to tetragonal phase transition and strong polaron effects. Using time-domain Brillouin spectroscopy, we demonstrate the efficient generation of coherent transverse acoustic phonons in the tetragonal phase of Cs2AgBiBr6 with amplitudes comparable to the longitudinal ones [1]. Notably, only one of the two TA modes is selectively excited, demonstrating a sharp temperature dependence of sound velocity near a structural phase transition at approximately 122 K. In cubic phase at the temperature above structural phase transition T > 122 K only longitudinal phonons are observed. The polarization of photoinduced transverse phonons in tetragonal phase is dictated by the projection of the c-axis on the surface plane, which leads to a prominent anisotropic polarization response in the detection.

The shear strain generation mechanism relies on anisotropic photostriction of crystal lattice and should be present in large variety of perovskites materials with tetragonal crystal symmetry. Anisotropic photostriction is directly related to the strong interaction of electrons with optical phonons in combination with crystallographic phase transition. Our findings highlight halide perovskites as promising materials for developing active hypersonic devices with tunable frequency and polarization of acoustic phonons.

References:

[1] Horiachyi, D.; Nestoklon, M. O.; Akimov, I. A.; et al. Efficient launch of shear phonons in photostrictive halide perovskites.

Acknowledgements:

The Dortmund andWürzburg groups acknowledge financial support from the Deutsche Forschungsgemeinschaft within
the framework of the SPP 2196 (Project No. 506623857). D.O.H. acknowledges the Deutsche Forschungsgemeinschaft
(Project No. 536987509). M.O.N. gratefully acknowledges the computing time provided on the Linux HPC cluster at
Technical University Dortmund (LiDO3), partially funded in the course of the Large-Scale Equipment Initiative by
the Deutsche Forschungsgemeinschaft (Project No. 271512359). N.V.S. and D.R.Y. acknowledge financial support of
the Deutsche Forschungsgemeinschaft via the Collaborative Research Center TRR142 (project A11).

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