[10a-Z23-1~8] 4.7 Quantum Optics and Nonlinear Optics

▲ [10a-Z23-4] Coherent Acoustic Phonons and Ultrafast Carrier Dynamics in Hetero-Epitaxial BaTiO₃-BiFeO₃ Films and Nanorods

〇(DC)Rathsara Rasanjalee Herath Mudiyanselage¹, Brenden A. Magill¹, John Burton¹, Moira Miller¹, Joseph Spencer¹, Kiara McMillan¹, Giti A. Khodaparast¹, Min Gyu Kang², Deepam Maurya², Shashank Priya^2,3, Jade Holleman^4,5, Steve McGill^4,5, Christopher J. Stanton⁶ (1.Department of Physics, Virginia Tech, 2.Center for Energy Harvesting Materials and Systems (CEHMS) and Bio-inspired Materials and Devices Laboratory (BMDL), Virginia Tech, 3.Materials Research Institute, Penn State, 4.National High Magnetic Field Laboratory, FL, USA, 5.Department of Physics, Florida State University, 6.Department of Physics, University of Florida)

Keywords:Multiferroic materials, Time-resolved differential reflectivity, Coherent acoustic phonons

Abstract: The improved coupling between electric, magnetic, optical, and structural order parameters found in multiferroic BaTiO₃-BiFeO₃, generate the desire to explore novel functionalities in these lead-free systems. In order to obtain information to develop high speed multifunctional devices, we performed time-resolved differential reflectivity measurements of (1-x) BaTiO₃ -(x) BiFeO₃, with x = 0.725 and BaTiO₃-BiFeO₃ nanorods. We report a quantitative study of ultrafast carrier dynamics in BaTiO₃-BiFeO₃, by diffusion of the photoexcited carriers away from the surface and that the ambipolar diffusion constant is below 1-2 cm²/s. We also report the detection of coherent acoustic phonons(CP) in both film and nanorod samples at lower temperatures (100 K). In the film sample, we estimated the CP frequency to be _~ 27 GHz. In the Nanorod sample, we observed a higher frequency oscillation and a lower frequency oscillation with a frequency of _~ 33 GHz and 8 GHz. We attributed Higher frequency oscillations to be coherent acoustic phonons and we explain two probable origins for the lower frequency case. The lower frequency is close to a theoretically predicted magnon frequency in BFO, but the strength of this oscillation only had a very weak magnetic field dependence. Another explanation for this feature could be multiple reflections of the acoustic phonons at the Pt interfaces due to the large acoustic impedance mismatch.