Charge and spin collective excitations in a coupled spin-polarized bilayer system

Abstract

We investigate the occurrence of charge and spin density collective excitations in a bilayer quasi-two-dimensional spin polarized system in the presence of interlayer tunneling. The inclusion of the self-consistent magnetization interaction among the electron spins, in addition to the Coulomb interaction, permits the resolution of coupled in-phase and out-of-phase electric and magnetic modes associated with the charge and spin densities in the two layers. While the in-phase modes are not affected by tunneling, the out-of-phase modes, both electric and magnetic, are gaped, the width of the gap being proportional to the tunneling amplitude. We analyze the existence of these modes outside the electron-hole continuum within the random phase approximation and suggest that they can be relevant for materials with large gyromagnetic factors, for example, dilute magnetic semiconductors.