Coulomb interaction mediated tuning of surface plasmon resonances in terahertz hole arrays

Abstract

Resonance excitation of surface plasmons in sub-wavelength periodic apertures (popularly known as hole arrays) is typically decided by its lattice configurations and constituent material characteristics. Therefore, the excitation frequency of surface plasmon resonances (SPRs) in hole arrays is not easy to alter without modifying these basic structural parameters. However, we experimentally demonstrate modulation of SPR frequency by carefully incorporating an additional hole of similar geometry. By suitably modifying the relative positions between the holes inside the unit cell (fixed lattice parameters), we have tailored the SPR excitation frequency. Predominantly, we attribute such frequency detuning to near-field Coulomb interactions in between the holes that can modify the effective permittivity of the hole arrays, hence SPR characteristics. In totality, our experiments demonstrate a 7.6% shift in the SPR frequency. Further, all the experimental findings are explained through elaborate electromagnetic simulations that helped to acquire deeper physical insights related to the SPR excitation. We believe such near-field effect-based resonance tuning can find potential applications in realizing SPR-based sensors, tunable filters, and tunable non-linear devices operating in the terahertz (THz) domain.