# Controllable Fano-like Resonance in Terahertz Planar Meta-Rotamers
## 2 Design and Methods  
Figure 1a shows a representative unit cell of the proposed metamaterial numerically simulated in this study. The two top virtual layers have two different types of meta-atoms, a C-shaped metallic split-ring resonator (SRR) with spatially varying geometric parameters and a Y-shaped metallic rod with different rotation angles. The meta-molecule shown in the lowest layer of Figure 1a can be considered a unit cell of composite metamaterials, produced by combining the SRR and the Y-shaped rod. The two types of meta-atoms are structurally combined to be an analog of rotational isomers (also called rotamers) in chemistry, in which the rotamers can be interconverted by rotations. By combining the rotating Y-shaped meta-atoms to the fixed SRR meta-atom, the arrangements of meta-atoms in a meta-molecule that are transformed by rotation about the central axis of bonding can be exploited to generate different conformations that provide a possible method to design promising THz devices. Figure 1: (**a**) Schematic of the THz planar meta-rotamer consisting of the C-shaped SRR and Y-shaped metal rod. The physical dimensions of the meta-molecules in the lattice are \(P_{x}=P_{y}=120\)\(\upmu\)m. The thicknesses of the meta-molecules and dielectric substrate (bare silicon) are 150 nm and 200 \(\upmu\)m, respectively. (**b**) Schematic of the Y-shaped meta-atom. The corresponding size and rotations are as follows: \(L=40\)\(\upmu\)m; \(\theta_{y}=0^{\circ}\), \(30^{\circ}\), and \(60^{\circ}\). (**c**) Schematic of the C-shaped SRR meta-atom. The corresponding size and angular gaps are as follows: \(D=100\)\(\upmu\)m; \(\theta_{c}=10^{\circ}\), \(20^{\circ}\), and \(30^{\circ}\). The basic components (C-shaped SRR and Y-shaped rod) display optimal characteristics for fabricating the composite metamaterials, which can also be called meta-rotamers. The Y-shaped meta-atom is one of the simplest structures showing polarization-insensitive transmission or absorption properties because of its higher-order rotational symmetry and folded-slot resonators; moreover, it is available to fabricate multimode resonators and active control devices [28; 29; 30; 31; 32; 33]. As shown in Figure 2a, the folded planar resonator consisting of two arms placed in the direction of polarization of the incident THz waves generates a dipole resonance with a resonant wavelength equal to twice the length of the metal rod [31]. When the Y-shaped meta-atom rotates, the three arms alternately assume the function of the folded planar resonator while exhibiting polarization-independent optical properties, as shown in the inset of Figure 2a. Here, the normalization was carried out by dividing the spectral amplitudes through the metamaterials by the spectral amplitude through bare silicon used as a substrate. The C-shaped SRR meta-atom leads to dramatic structure-dependent features. The tunability of optical resonances can be achieved by varying the arc length of the C-shaped, polarization-dependent characteristics due to high structural asymmetry, and the fabrication of composite medium with simultaneously negative values of effective permeability and permittivity. As a result, versatile and novel optical devices can be realized, such as negative refractive index devices, superlenses, multifunctional filters, polarization devices, and various types of resonators [34; 35; 36; 37; 38]. Figure 2b shows the simulated THz amplitude spectra in the arrays of C-shaped SRR meta-atoms with angular gaps of \(\theta_{c}=10^{\circ}\), \(20^{\circ}\), and \(30^{\circ}\). As the total arc length of the C-shape is shorter, the two odd resonances are blue-shifted because the resonance wavelength depends on the arc length of the C-shape. As in the aforementioned case, when the polarization of the incident light at normal incidence is parallel to the gap of the C-shaped SRR, the two odd resonances appearing near the frequencies of 0.25 THz and 0.7 THz can be clearly observed.