Temperature and magnetic field tunability of composite metamaterials containing spherical semiconductor particles in far-infrared and terahertz regimes

The effect of temperature and dc magnetic field variations on effective electromagnetic parameters of metamaterials (MTMs) containing spherical semiconductor particles is studied theoretically. The effect of temperature is taken into account through its influence on semiconductor carrier density and mobility. The effect of dc magnetic field is included using an extension of the Mie theory, describing the interaction of a plane wave with a gyrotropic sphere. The effective parameters such as relative permittivity and permeability are calculated by proper application of the Maxwell Garnett (MG) theory and its extensions to quasi-static condition and multi-phase structures. Based on these theories, the temperature and dc magnetic field tunability of three different MTM structures is investigated. First a single phase medium is considered which contains spherical semiconductor particles of one kind, randomly dispersed in a dielectric host. Then two multi-phase structures containing (a) two kinds of spherical semiconductor particles or (b) spherical particles with core-shell topology are investigated. The two multi-phase MTM structures can exhibit negative index of refraction in far-infrared spectral region. The measure of the temperature and dc magnetic field tunability of effective parameters such as relative permittivity and refractive index of the structures is evaluated and it is shown specifically that the real part of refractive index can be tuned to get negative, zero or positive values in far-IR or THz regimes, but the imaginary part of the index and the Figure of Merit (FOM) are also quite sensitive to the temperature and magnetic field variations. The tunable MTMs can find new applications in THz devices such as switches, tunable mirrors, isolators, converters, polarizers, filters and phase shifters.