Abstract
A terahertz (THz) electromagnetically-induced transparency (EIT) phenomenon is observed from two types of self-complementary meta-molecules (MMs) based on rectangular shaped electric split-ring resonators (eSRR) on Croatian checkerboard. Each MM contains a couple of identical size eSRRs and a couple of structural inversed eSRRs twisted π/2 in checkerboard pattern. In the first type of MM (type-I), the gap is in the middle line of eSRR. In the second type of MM (type-II), the gap is on the two arms of eSRR. Both types of MMs exhibit EIT effect. A maximum 20 ps group delay is observed at the transparency window of 0.63 THz in type-I MM; while a maximum 6.0 ps group delay is observed at the transparent window of 0.60 THz in type-II MM. The distribution of surface currents and electrical energy reveals that only CeSRR contribute to the transparency window as well as the side-modes in type-I MM, where the current leakage via contact point contributes to the low-frequency side-mode, and the coupled local inductive-capacitive (LC) oscillation in CeSRRs contributes to the high-frequency side-mode. In type-II MM, however, the localized dipolar oscillator of CeSRR contributes to the low-frequency side-mode; while the hybridization of dipole oscillation on eSRR and LC resonance on CeSRR contributes to the high-frequency side-modes. Our experimental findings manifest a new approach to develop THz slow-light devices.
Highlights
Maxwell equations indicate that the electric field (E) is the dual of the magnetic field (H)
The transparency window vT mode is constructed by the side-mode vL and vH, where the local inductive-capacitive (LC) mode on electric SRR (eSRR) does not contributes to the generation of electromagnetically-induced transparency (EIT)
An EIT phenomenon at THz frequency band is observed in self-complementary MMs in Croatian checkerboard
Summary
Maxwell equations indicate that the electric field (E) is the dual of the magnetic field (H). It is found that the to of metal structural MM achieve minimum, while the tc of structure inversed or complementary MM achieves maximum. Owing to this phenomenon, the metal resonators and its complementary resonators can be integrated in one unit cell, which is termed as self-complementary MMs. There are many works on the extra-ordinary response of manipulating electromagnetic wave using self-complementary MMs, such as negative permittivity and permeability[3], frequency-independent response[4], asymmetric transmission[5], polarization conversion[6,7], flat band-filter[8], invisible cloaking[9] controllable Smith-Purcell effect[10], and travelling wave manipulation in accelerator[11]. Owing to the Babinet’s principle, the central frequency of resonance minimum of the originally metal resonator to must be identical to that of the resonance maximum of the corresponding inversed structures tc. The origin of the transparency windows as well as the slow light effect is revealed by numerically mapping the electromagnetic field and the surface current at the frequencies of transparency windows as well as the side-modes
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