High Optical Performance and Practicality of Active Plasmonic devices based on Rhombohedral BiFeO$_3$*

BiFeO$_3$ is a multiferroic oxide with perovskite type structure, which has been studied extensively for its ferroelectric and magnetic behavior. The magnetoelectric coupling could potentially provide new functionalities. We have studied the electronic and optical properties of Rhombohedral BiFeO$_3$, which we show to be a very promising candidate material to build active nanophotonic devices, in particular nanoplasmonic devices. It has a strong switching modulated optical properties and a large optical birefringence $\Delta $n arising from the combination of octahedral tilts, ferroelectricity and G-type antiferromagnetism in BiFeO$_3$. A prototype of a plasmonic resonator with a Rhombohedral BiFeO$_3$ thin film layer is used as an example and shows excellent switch and modulation responses. The proposed approach provides potential opportunities to develop high performance nanophotonic devices for optical communication. We find excellent switching and modulation responses. The use of Rhombohedral BiFeO$_3$ provides an effective way to actively control optical performance of plasmonic nanostructures.