Collective Modes in Graphene on a Bulk Substrate

Description

Intensive research on graphene for over a decade has been aimed at improving various existing technologies, spanning the wide range of electrical, optical, thermal, filtering and mechanical applications. In optics, nanophotonic devices require the electromagnetic energy confined to below the diffraction limit, as achieved in plasmonic excitations. Fei et al [1] used scattering-type scanning near-field optical microscopy (s-SNOM) to measure graphene’s Dirac plasmon for wave vectors q as large as 3 · 109 /cm. For these collective excitations we here explore the fundamental properties, resulting from the characteristic linear energy dispersion near the high-symmetry-points of the Brillouin zone. First, the complex dielectric function is obtained for freestanding graphene in the random phase approximation (RPA). The large plasmon damping due to interband excitations inevitably leads to the question of how collective modes are properly defined for short lifetimes; we here critically discuss the ambiguous definitions in the literature. Next, the above dielectric function together with that of the substrate is invoked in the calculation of the Fresnel coefficient for p-polarized light reflected by a graphene monolayer on SiO2 . The interaction with the substrate leads to coupled plasmon-phonon modes, as level-crossings must be avoided. Finally, we briefly present preliminary studies including spin-orbit coupling (of both, intrinsic and Rashba type). Such contributions to the Hamiltonian split the conduction and valence bands, implying characteristic modifications of graphene’s dielectric response function which will, in turn, significantly change the s-SNOM reflectivity. [1] Z. Fei et al., Nano Lett. 11, 4701 (2011)

Period	12 Sept 2018
Event title	68th Annual Meeting of the Austrian Physical Society
Event type	Conference
Location	AustriaShow on map