Photoexcitation of gigahertz longitudinal and shear acoustic waves in BiFeO₃ multiferroic single crystal

Using femtosecond laser pulses, coherent GHz acoustic phonons are efficiently photogenerated and photodetected in BiFeO₃ (BFO) multiferroic single crystal. Due to the crystal lattice symmetry, longitudinal as well as two transverse acoustic modes are generated and detected, and the corresponding sound velocities are determined. This provides the opportunity to experimentally evaluate the elastic coefficients of the multiferroic compound BiFeO₃ that have been estimated so far only through ab initio calculations. The knowledge of the elastic properties of BFO is highly desired for BFO integration in nanoelectronic devices. Moreover, our findings highlight also that BFO may be a good candidate for light-controlled coherent acoustic phonons sources.