Collective excitations in 2D materials

Research on 2D materials has been one of the fastest-growing fields in condensed matter and materials science research in the past 10 years. The low dimensionality and strong correlations of 2D systems give rise to electronic and structural properties, in the form of collective excitations, that do not have counterparts in ordinary 3D materials used in modern technology. These 2D materials present extraordinary opportunities for new technologies, such as in flexible electronics. In this Review, we focus on plasmons, excitons, phonons and magnons in 2D materials. We discuss the theoretical formalism of these collective excitations and elucidate how they differ from their 3D counterparts. 2D materials host various collective excitations, which either mutate or cease to exist in the bulk. In this Review, we select the most striking properties of 2D plasmons, excitons, phonons and magnons, contrasting them with the bulk versions.