  We have developed an analytical formulation to calculate the plasmon
dispersion relation for a two-dimensional layer which is encapsulated within a
narrow spatial gap between two bulk half-space plasmas. This is based on a
solution of the inverse dielectric function integral equation within the
random-phase approximation (RPA). We take into account the nonlocality of the
plasmon dispersion relation for both gapped and gapless graphene as the
sandwiched two-dimensional (2D) semiconductor plasma. The associated nonlocal
graphene plasmon spectrum coupled to the "sandwich" system is exhibited in
density plots, which show a linear mode and a pair of depolarization modes
shifted from the bulk plasma frequency.
