Propagation of Surface Plasmon Polaritons in Thin Films of Topological Insulators

Surface Plasmon Polaritons (SPP) are coupled collective oscillations of surface charges and electromagnetic waves confined to the interface between a metal and a dielectric. Three dimensional topological insulators (TI), such as Bi$_2$Se$_3$, Bi$_2$Te$_3$, and Sb$_2$Te$_3$ are narrow band-gap semiconductors in the bulk while having conducting surface with the linear energy dispersion for the surface electronics states. Similar to double-layered graphene a thin single film of TI supports two SPP modes in the far-infrared range. We study the propagation of these modes in thin films of Bi$_2$Se$_3$, Bi$_2$Te$_3$, and Sb$_2$Te$_3$. The dispersion curves and the propagation lengths are estimated for all three materials. The explanation of the discrepancy between the theory [1] and the first experimental observation of standing wave SPPs in Bi$_2$Se$_3$ [2] is proposed. Finally, the possibilities of tuning the SPP dispersion relations in thin films of TI are discussed.\\ $\lbrack 1\rbrack$ T. Stauber, G. Gomez-Santos, and L. Brey, Phys. Rev. B 88, 205427 (2013).\\ $\lbrack 2\rbrack$ P. Di Pietro, M. Ortolani, O. Limaj, A. Di Gaspare, V. Giliberti, F.\\ Giorgianni, M. Brahlek, N. Bansal, N. Koirala, S. Oh, P. Calvani, and S. Lupi, Nature Nanotechnology 8, 556 (2013).