Tunable wavelength dependent nanoswitches enabled by simple plasmonic core-shell particles

In this paper we demonstrate the feasibility of using a plasmonic core-shell particle to function as a wavelength dependent switch for integration into nanoantenna structures. First, a quasistatic analysis is performed and the necessary conditions are derived which allow the particle to operate in either a short- or an open-circuit state. These conditions dictate that the core and the shell permittivity values need to have opposite sign. Consequently, at optical wavelengths where noble metals are modeled as Drude dielectrics, these conditions can be easily realized. As a matter of fact, it is demonstrated that a realistic core-shell particle can exhibit both the short- and open-circuit states, albeit at different wavelengths. Our analysis is extended by examining the same problem beyond the quasistatic limit. For this task we utilize an inhomogeneous spherical transmission line representation of the core-shell particle. The conditions are derived for the particle that yield either an input admittance or impedance equal to zero. It is further demonstrated that these conditions are the short wavelength generalization of their quasistatic counterparts.