Energy shift of collective modes in spin-imbalanced graphene on SiO$_2$ from spin-sensitive linear response theory

The growing precision of optical and scattering experiments necessitates a better understanding of the influence of damping onto the collective mode of sheet electrons. As spin-polarized systems are of particular interest for spintronic applications, we here report spin-sensitive linear response functions of graphene, which give access to charge- and spin-density related excitations. We further calculate the reflectivity of graphene on an SiO 2 surface, a setup used in s-wave scanning near field microscopy. Increasing the partial spin-polarization of the graphene charge carriers leads to a significant broadening and shift of the plasmon mode, due to single-particle interband transitions of the minority spin carriers. We also predict an antiresonance in the longitudinal magnetic response function, similar to that of semiconductor heterostructures.