Giant electro-optic effect of plasmonic nanorod suspensions in the THz frequency range

We suggest theoretically that a plasmonic suspension with well-separated and randomly dispersed metal nanorods can exhibit a giant electro-optic (EO) effect in the THz frequency range. Due to the motion of free electrons, the metal nanorod with micrometer-scale length can be polarized efficiently by a static electric field, with an induced dipole moment 6 orders of magnitude larger than the inherent one of polar molecules. Moreover, the metal nanorod exhibits a plasmonic resonance in the THz band, and the THz optical polarizability (off resonance) of the nanorod can be increased by 12 orders of magnitude compared with the molecules. The orientation of nanorods with the static field changes the THz optical response of the plasmonic suspension and thus results in efficient EO, birefringence, and electro-absorption effects. Our calculation results show that, with a low static field of ∼10 V/mm, a huge refractive-index modulation of Δn∼1 (Δn/n = 56%) can be achieved. The results may offer new opportunities for designing artificial EO materials and constructing novel THz EO devices.