Ultrafast photo-acoustics in bulk perovskite semiconductor crystals

• Applicant: Dr. Dmytro Horiachyi
• Subject Area: Experimental Condensed Matter Physics ; Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 536987509

High frequency acoustic phonons in the spectral range from 10 GHz and larger can be used for fast manipulation of optical, electronic and magnetic properties in solid state. In this regard, perovskite semiconductors represent particularly interesting system which combines excellent optical properties and large variety of structural phase transitions. The main aim of this project is to explore the new aspects of phonon physics in bulk perovskites semiconductors and to establish efficient light-induced generation of coherent phonons in bulk perovskite semiconductors using a sequence of fs laser pulses. We will focus on direct and indirect band gap materials such methylammonium lead iodide and lead-free non-organic double perovskites which undergo phase transition from cubic to tetragonal phase with lowering the temperature. At first stage we will investigate the elastic properties close to structural phase transitions, where softening of the lattice leads to significant modification of the phonon frequencies. Next, we will elaborate the microscopic mechanisms for optical generation of high frequency coherent phonons with femtosecond laser pulses, where excitation of electron-hole pairs should play important role. Finally, we will focus on periodic optical excitation and test the tunability of the source of coherent phonons by varying the laser pulse repetition rate by a few orders of magnitude from 80 MHz up to ultimate frequency of 10GHz. The dynamics of phonons will be studied using time resolved pump-probe technique with micrometer spatial resolution. The latter includes combination with polarization resolved Brillouin spectroscopy, which will be used to evaluate the elastic and elasto-optical properties of the perovskite semiconductor and probe the spectrum of non-equilibrium phonons in case of excitation with fs pulses. The obtained results will significantly contribute to the development of optically driven source of coherent phonons in perovskite semiconductors and initiate novel photonic and optoelectronic devices.

• DFG Programme: WBP Position