Impacts of electric gating and divacancies on optical absorption spectra of zigzag buckling silicene nanoribbons

In this study, by combining the tight-binding description with the gradient approximation, we investigated the impacts of electric gating and divacancies on the optical characteristics of zigzag buckling silicene nanoribbons. Our results show that the back-gate electric potential tends to shift the peak structure to higher frequencies in the free-defective structures, while the side-gate electric potentials intensify the intensity of the excitation channels obeying the selection rule $\Delta J=\text{even}$. In particular, applying the potentials in a suitable range can improve the optical absorption efficiency at a certain frequency with the back gate or widen the threshold absorption intensity from $J^v=1$ to $J^c=1$ with the side gates. Besides, the defective structures' absorption spectra exhibit richer features than the perfect one, with the appearance of new optical excitations due to the transitions between the local minimum or maximum in the low-energy bands around the Fermi level. Moreover, applying electric gating in defective structures can also tune the absorption spectra with additional features.