Fig. 4: Intrinsic plasmons in graphene and 3D topological insulator.
From: Two-dimensional Dirac plasmon-polaritons in graphene, 3D topological insulator and hybrid systems
a s-SNOM signals s(ω,x) at 0 ps are shown as a function of distance L from the hBN/G/hBN boundary. b s(ω,x) at 2 ps. c, d The spatial derivatives ds(ω,x)/dx are shown at 0 ps (c) and 2 ps (d). e Schematic illustration of Bi2Se3 bandstructure with topological surface state (TSS), bulk conduction band (BCB), and bulk valence band (BVB). f 30 QL Bi2Se3 microribbons is grown on (Bi0.5In0.5)2Se3/Al2O3. The electric-field polarization of the THz-pump (THz-probe) is parallel (perpendicular) to the microribbon’s direction. The width of the microribbon L0 is 4, 8, and 20 μm. g Spectral extinction (circles) are shown with fit lines (solid red line) at different L0. The fit lines are composed of the phonon-dressed plasmon (blue dashed line) and the bare plasmon extinction (orange dashed line). h Pump-induced change in the extinction (circles) are shown with fit lines (solid red line) at different L0. The plasmon extinction shifts from equilibrium (blue dashed line) to non-equilibrium (orange dashed line). The imaginary part (right column) is obtained from Kramers-Kronig relation of the real part (left column). i The TSS chemical potential μ(Te) is plotted as a function of the electron temperature Te. j The Bi2Se3 plasmon frequency νpl at Te = 78 K (black dots) and Te = 1430 K (red dots) are displayed as a function of the plasmon wavevector k = π/L0. The simulations (black and red lines) are performed at corresponding Te. a‒d Adapted with permission from ref. 55, Springer Nature. e‒j Adapted with permission from ref. 57, American Physical Society
