Geometry- and field-diversified electronic and optical properties in bilayer silicene

The generalized tight-binding model has been developed to thoroughly explore the essential electronic and optical properties of AB-bt bilayer silicene. They are greatly diversified by the buckled structure, stacking configuration, intralayer and interlayer hopping integrals, spin-orbital couplings; electric and magnetic fields (${E_z\hat z}$ $\&$ ${B_z\hat z}$). There exist the linear, parabolic and constant-energy-loop dispersions, multi-valley band structure and semiconductor-metal transition as $E_z$ varies. The $E_z$-dependent magnetic quantization exhibits the rich and unique Landau Levels (LLs) and magneto-optical spectra. The LLs have the lower degeneracy, valley-created localization centers, unusual distributions of quantum numbers, well-behaved and abnormal energy spectra in $B_z$-dependences, and the absence of anti-crossing behavior. A lot of pronounced magneto-absorption peaks occur at a very narrow frequency range, being attributed to diverse excitation categories. They have no specific selection rules except that the Dirac-cone band structures are driven by the critical electric fields. The optical gaps are reduced by $E_z$, but enhanced by $B_z$, in which the threshold channel might dramatically change in the formed case. The above-mentioned characteristics are in sharp contrast with those of layered graphenes.