Collective spin oscillations in a magnetized graphene sheet

Abstract

We investigate collective spin excitations of graphene electrons with short-ranged interactions and subject to the external Zeeman magnetic field. We find that in addition to the familiar Silin spin wave, a collective spin-flip excitation that reduces to the uniform precession when the wave's momentum approaches zero, the magnetized graphene supports another collective mode visible in the transverse spin susceptibility: a collective spin-current mode. Unlike the Silin wave, this mode is not dictated by the spin-rotational symmetry but rather owns its existence to the pseudo-spin structure of the graphene lattice. We find the new collective excitation to become sharply defined in a finite interval of wave's momenta, the range of which is determined by the interaction and the magnetization.