Tunable high-Q resonance and abnormal phase-shift in P T-symmetric meta-molecules

We analyze the optical response of a parity-time ( P T ) symmetric diatomic meta-molecular array. We show that the P T symmetry can transform an initial dark antisymmetric mode of the diatomic meta-molecule into bright, featured by a high- Q peak in the scattering spectrum. The Q factor is tunable by managing the magnitudes of the gain and loss. Furthermore, around this high- Q resonance an abnormal phase-shift is obtained, which persists even at exceptional point. We also show that the effective dielectric constant of the P T -symmetric meta-molecular array can be modeled by an anomalous doubly-resonant Lorentz oscillator, which is different from that in electromagnetically induced transparency and Autler-Townes splitting. This study contributes to the advances of non-Hermitian optics and slow light.