Resonance excitation of surface plasmons in sub-wavelength periodic apertures (popularly known as hole arrays) is typically decided by its lattice configurations and the 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.

Metal-based magnetic multilayers are primarily responsible for giant-magnetoresistance (GMR) that play a pivotal role in magnetic memory devices besides other spintronic applications. Spin-dependent conduction of electrons steered by spin-dependent scattering across interfaces of the ferromagnetic (FM)/nonmagnetic multilayers lies at the core of GMR phenomena. In this context, the thickness dependent magnetoresistive effect in five-layer Al/Ni/Al/Ni/Al spin valve structures is explored through contactless terahertz (THz) spectroscopy. Our experiments reveal magnetic field dependent conductivity enhancement in the multilayer configuration of a FM (nickel, Ni) layer and a nonmagnetic (aluminum, Al) spacer layer under the application of relatively low intensity magnetic fields (0–30 mT) manifesting a substantial ground for low power THz magnetism. In addition, influence of similar magnetic fields is probed for relatively thicker spacers (10 nm ≤ x ≤ 20 nm) that can form a platform for dynamically controllable THz devices. Our studies demonstrate a maximum THz peak amplitude modulation of around 48% for a 10 nm thick nonmagnetic spacer layer (Al layer) along with a significant relative modulation (∼97%) in THz conductivities. Such tuning of THz characteristics bears great potential in realizing dynamically reconfigurable THz and magnetoresistive devices by suitably exploiting multilayer spin valve configuration.