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

The temporal physical behavior of multifunctional materials such as multiferroics after the laser irradiation has been very intriguing in recent years. Here, the ultrafast carrier dynamics of the multiferroic BiFeO3 film in a broad temperature range is investigated using optical pump-probe spectroscopy. The photoexcited electrons in BiFeO3 release their energy through coupling with the longitudinal-optical phonons (~ 1 ps) and with the magnetic lattice (several ps). The temperature dependences of the peak value of the optical reflectivity and the time constants of carrier relaxation channels show significantly changes from 137.5 K to around 195 K, which is in accordance to the previously reported hidden phase transition. Our study demonstrates that ultrafast spectroscopy is a sensitive method to look insight into the dynamical interactions among the on-site high-energy electrons accumulated in the p conduction band of Bi, coherent optical phonon, and the magnetic lattice.