Fano-resonance collapse induced terahertz magnetic dipole oscillation in complementary meta-atoms via local symmetry breaking.

A novel phenomenon is observed in the meta-atoms composed of a complementary rectangular double split-ring resonator (SRR). An intrinsic Fano-resonance collapses with the outer SRR deformed asymmetrically. Alternatively, a trapped mode emerges at an adjacent frequency region, of which its strength grows up with increasing the asymmetric deviation. However, the asymmetric deformation in the inner SRR has influence neither on the evolution of this intrinsic Fano-resonance nor on the excitation of the aforementioned trapped mode. The results of electromagnetic field simulation indicate that an interference of two magnetic dipoles leads to the intrinsic Fano-resonance on the outer SRR. The asymmetric deviation destructs coherent interference so that the Fano-resonance collapses. To the trapped mode, the surface current passes through the metal gap of the outer SRR, leading to a couple of antiparallel currents, which results in a couple of magnetic dipole oscillations. The intrinsic modes are kept constant, even though the inner SRR is asymmetrically deformed. The outer SRR plays the role of a Faraday cage, which electromagnetically shields the trapped mode on the inner SRR. [ABSTRACT FROM AUTHOR]