Structural dependent ultrafast electron-phonon coupling in multiferroic BiFeO3 films

The electronic energy relaxation of polycrystalline BiFeO3 films is studied using ultrafast pump-probe spectroscopy. After photo-excitation with femtosecond laser pulses, the relaxation of hot electrons is identified to decay with two different characteristic times. The fast process is attributed to scattering of electrons with lattice-vibration modes, and the slow one is corresponding to the spin-lattice thermalization. The electron-phonon coupling is characterized by the second moment of the Eliashberg function, λ〈ω2〉. Due to the structural strain and symmetry breaking, the electron-phonon interaction strength of tetragonal BiFeO3 films is larger than that of rhombohedral counterparts.