Small Polaron-induced Ultrafast Ferroelectric Relaxation in BiFeO₃

BiFeO₃ (BFO) has been identified as a ferroelectric material and has been widely applied in the fields of energy harvesting and optoelectronics. However, unraveling the critical lattice movements and charge distribution responsible for the ferroelectric behavior in BFO still remains a challenge. In this talk, I will discuss the ultrafast XUV spectroscopy and ultrafast SFG spectroscopy measurements that directly monitoring the evolution of ferroelectric properties in BFO upon optical excitation. Our finding suggests that the small polaron formation involved with optical phonons play a pivotal role in the ultrafast relaxation of ferroelectric and the acoustic phonon involved shear strain contribute to the subsequent recovery of ferroelectric at longer time scale. Additionally, our results showed that the ultrafast electronic dynamics is irrelevant to the ferroelectric properties.