Structural dependent ultrafast electron-phonon coupling in multiferroic BiFeO3 films

Abstract

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.

Strain modulated transient photostriction in La and Nb codoped multiferroic BiFeO3 thin films

“…Extracted by a bi-exponential decay function, the electron-phonon thermalization time constant has been found to be sensitive to the structure of the BFO film sample. 23 Sheu et al analyzed the subsequent slow relaxation with different optical excitation energies and found that the photo-excited electrons primarily leave the conduction band via radiative recombination. 24 Here, we concentrate on the appearance of the periodic oscillations during the slowrelaxation process.…”

Temperature dependent photoexcited carrier dynamics in multiferroic BiFeO3 film: a hidden phase transition

“…28, rather than previously regarded tetragonal structure. 27,29 However, comparing with bulk BiFeO 3 with a rhombohedral structure, a slight shifting of (012) h diffraction peaks to lower 2h angles was observed, which indicates a trend of distortion toward to tetragonal structure.…”

“…[31][32][33] The peak amplitude at zero time delay linearly depends on the number of the photoexcited electrons, as evidenced by the experiment performed at different pump fluence. 27 As shown, the DR(t)/R marked by two dashed lines in Fig. 2(a) following the initial photo-excitation.…”

“…5,25,26 In our previous work, we have observed the electron-phonon interaction of BiFeO 3 thin film at room temperature. 27 In this Letter, we are interested in the phase transition by characterizing the coupled magnetic and ferroelectric orders in epitaxially grown BiFeO 3 thin film on SrTiO 3 (STO) substrate, through the ultrafast optical pump-probe spectroscopy. The temperature dependent transient differential reflectivity (DR(t)/R) allows us to disentangle the different carrier relaxation dynamics in separated phases of BiFeO 3 .…”

“…The pump pulse with the energy of 3.1 eV is larger than the band edge transition (E g $ 2.48 eV) of BFO film. 27 The pump energy corresponds to a minority dipole-allowed oxygen-iron charge transfer excitation and a strongly hybridized majority channel of O 2p þ Fe 3d ! Bi 6p state excitation.…”