## 4 Active Switching of Fano Resonances
The initial cooling does not effectively affect the Fano resonance of both Fano 1 and Fano 2 until the temperature dropped to about 60 \({}^{\circ}\)C. The Fano resonances are gradually switched off with the decrease of external temperature. When the temperature dropped to 55 \({}^{\circ}\)C, the Fano resonance completely disappears. The simulated two-dimensional plot clearly shows that compared with the heating process, it is not easy to switch off the Fano resonance by cooling the structure. That is to say, the switch process of Fano resonance realized by utilizing the temperature control is not reversible. Herein, it should be highlighted that the active switching of Fano resonance can be realized by using very low heat pump closest to the room temperature, which is difficult to obtain in other tunable Fano devices. The simulation results demonstrate the highly temperature-sensitive nature of the sharp Fano resonances to the external thermal stimulus. We preliminarily predict that the observed active switching of sharp Fano resonance is closely associated with the change in the conductivity of VO\({}_{2}\) film embedded MM structures. For the heating process, at low temperature, VO\({}_{2}\) behaves as insulator with low conductivity and is transparent to incident THz waves. Thus, the proposed MM structure is equivalent to the symmetrical double-C shaped periodic array composed of gold, which can generate the eigen resonance mode excited by the dipole resonance. As the increasing pump temperature, the number of carriers in VO\({}_{2}\) material increases, which results in the sharp increase in conductivity. Hence, the phase changed VO\({}_{2}\) rectangular strips in the designed MMs play a role of quasi-metals with a skin depth around 1 \(\upmu\)m at 1.0 THz. This change of VO\({}_{2}\) destroys the symmetry of the double-C shaped MM structures and excites the double Fano resonances. However, Fano resonance induced by cooling process is completely different. The main reason for this phenomenon is that the IMT temperatures of VO\({}_{2}\) in the process of heating and cooling are quite different, which are 68 \({}^{\circ}\)C and 64 \({}^{\circ}\)C, respectively, leading to different regulation behavior of the metadevice. In addition, there is an obvious physical phenomenon in Figures 3 and 4 that cannot be ignored, that is, at low temperature (45 \({}^{\circ}\)C), we have not only observed an eigen resonance mode in the whole  
Figure 4: Two-dimensional graph of simulated THz transmission spectra corresponding to frequency and temperature of the proposed VO\({}_{2}\)-implanted MM structures, describing the continuously tunable process of Fano 1 and Fano 2: (**a**) heating process; (**b**) cooling process. spectrum, but also two sharp micro resonance dips with low transmission at 0.635 THz and 1.295 THz. It can be explained as follows: Although VO\({}_{2}\) behaves as an insulator at low temperature, it is still not completely transparent to THz waves and has a small loss, which destroys the symmetry of the structure a little and produces the two small Fano resonance dips. From another point of view, this physical phenomenon also further confirms the physical mechanism of Fano resonance excited by the asymmetry of the MM structure.