Observation of Dirac plasmons in a topological insulator

Abstract

Plasmons are quantized collective oscillations of electrons and have been observed in metals and doped semiconductors. The plasmons of ordinary, massive electrons have been the basic ingredients of research in plasmonics and in optical metamaterials for a long time. However, plasmons of massless Dirac electrons have only recently been observed in graphene, a purely two-dimensional electron system. Their properties are promising for novel tunable plasmonic metamaterials in the terahertz and mid-infrared frequency range. Dirac fermions also occur in the two-dimensional electron gas that forms at the surface of topological insulators as a result of the strong spin-orbit interaction existing in the insulating bulk phase. One may therefore look for their collective excitations using infrared spectroscopy. Here we report the first experimental evidence of plasmonic excitations in a topological insulator (Bi2Se3). The material was prepared in thin micro-ribbon arrays of different widths W and periods 2W to select suitable values of the plasmon wavevector k. The linewidth of the plasmon was found to remain nearly constant at temperatures between 6 K and 300 K, as expected when exciting topological carriers. Moreover, by changing W and measuring the plasmon frequency in the terahertz range versus k we show, without using any fitting parameter, that the dispersion curve agrees quantitatively with that predicted for Dirac plasmons.

Tight-binding methods for general longitudinally driven photonic lattices: Edge states and solitons

“…The pseudo-field, A(z), is defined in Eq. (10). The physical parameters chosen in the simulations below are presented in Table I and reflect the experimental setup used in [5].…”

“…Some of the recent advances in topologically protected systems include: PT symmetry crystals [7], bianisotropic metamaterials [8,9] and surface plasmons [10]. Higher-dimensional systems have also been examined [11], where the 3D analog of Dirac points called Weyl points have been reported [12,13].…”

Plasmons in topological insulator cylindrical nanowires

“…Only recently, Dirac magneto-plasmons were observed in TI showing high frequency tunability in the mid-infrared and terahertz spectral regions [14][15][16][17][18] . Due to the spin-momentum locking 19,20 , these plasmons are always coupled to spin waves acquiring a spin character.…”

Stability of low-carrier-density topological-insulator Bi2Se3 thin films and effect of capping layers

“…7,12 The relative stability of these high-carrier-density samples has helped attaining numerous consistent results across different probing techniques even without any special care to protect the surface layers. 9,13 In contrast, recently developed low-carrier-density bulk-insulating Bi 2 Se 3 films 14,15 exhibit quite significant aging effect in air. The as-grown sheet carrier densities of these samples are about an order of magnitude lower than the previous generation samples.…”