Negative refractive index enhancement with zero absorption in a concentric chiral metal-atomic nanoshell

Abstract

We investigate the electromagnetic chirality and negative refraction in a concentric nanoshell of a chiral metal sphere and a chiral atomic shell. The medium of the atomic shell with a four-level system is driven by a laser field and an incoherent pump field in a diamond configuration. We show that the electric and magnetic absorption spectra connecting through the chiral coefficients of the respective dipole moments of the two media, produce five and three lines spectral profiles. We explain that the spectral lines separated by dips are the manifestation of classical (quantum) coherence effect of the wave field excitation in the medium of the metal sphere (atomic shell), and interaction of the respective dipole moments at the interface of the two media. Furthermore, we show negative refraction with zero absorption without requiring permittivity (ε) and permeability (µ) simultaneously negative, where for all values of the incident wavelength, Re[µ] ≈ 1, representing a strong chiral electromagnetic behavior. Consequently, the negative refractive index enhances sufficiently beyond n = -1 for a wide range of parameters depending on the coupling parameters, chiral coefficients and, on the radii ratio of the concentric metal-atomic nanoshell .