Feature-rich electronic excitations of silicene in external fields

We develop a generalized tight-binding model to investigate the Coulomb excitations in monolayer silicene. The atomic interactions, spin-orbit coupling, magnetic and electric fields, as well as the Coulomb interactions are simultaneously included in our calculations. The magnetic field induces interband plasmons with discrete frequency dispersions restricted to quantized energy states. An intraband plasmon, with a higher intensity and continuous dispersion relation, exists in the presence of free carriers. This mode is dramatically transformed into an interband plasma excitation when the magnetic field is increased, leading to abrupt changes in the value of the plasma frequency and its intensity. Specifically, an electric field may separate the spin and valley polarizations and create additional plasmon modes, a unique feature arising from the buckled structure and the existence of noteworthy spin-orbit coupling.