Study of Spin-Polarization Effects of Collective Excitations in Double-Layer GrapheneStructures

We investigate plasmon properties in a double-layer graphene structure under the effects of an in-plane external magnetic field within the zero-temperature random-phase approximation. Numerical calculations demonstrate that two plasmon modes exist in the system, corresponding to in-phase and out-of-phase oscillations of charges. The spin polarization number P affects the optical and acoustic plasmon modes and their decay rate differently. As the polarization number increases, the frequency of the acoustic mode slightly decreases while that of the optical mode significantly increases. Besides, the existence of an external magnetic field expands the single-particle-excitation area of the system; therefore, plasmon modes become damped at a smaller wave vector, compared to those in the case of unpolarized systems. The separation between two layers increases (decreases) the plasmon frequency of the acoustic (optical) mode. Finally, we found that background dielectric inhomogeneity decreases the energy and decay rate of plasmon modes of the spin-polarized system.