Dynamically controllable terahertz metamaterial based on annealed and unannealed BiFeO₃ thin film on Si

We theoretically and experimentally study a terahertz metamaterial based on a hybrid metamaterial/BFO/Si structure, where the BFO thin films are annealed and unannealed, respectively. Due to the interaction or hybridization of two resonators, an obvious plasma-induced transparency effect can be obtained in the transmission spectra. With increasing the external optical pumping power, the transparency peak modulation depth of the annealed hybrid sample is about 45% while the unannealed hybrid sample is almost zero. The annealing treatment has a significant effect on the modulation through investigating the photoconductivity of the BFO thin films. The photogenerated carriers suppress the resonances of the two bright modes, thus the transparency peak of the metamaterial is disappeared. This work is a further step forward in practical applications of BFO-based terahertz functional devices and a path for exploration of multiferroic material BiFeO₃ in the terahertz range.