Interaction of edge exciton polaritons with engineered defects in the hyperbolic material Bi2Se3

Abstract

Hyperbolic materials exhibit unique properties that enable intriguing applications in nanophotonics. The topological insulator Bi2Se3 represents a natural hyperbolic optical medium, both in the THz and visible range. Here, using cathodoluminescence spectroscopy and electron energy-loss spectroscopy, we demonstrate that Bi2Se3 supports room-temperature exciton polaritons and explore the behavior of hyperbolic edge exciton polaritons, which are hybrid modes resulting from the coupling of the polaritons bound to the upper and lower edges of Bi2Se3 nanoplatelets. We compare Fabry-Pérot-like resonances emerging in edge polariton propagation along pristine and artificially structured edges and experimentally demonstrate the possibility to steer edge polaritons by means of grooves and nanocavities. The observed scattering of edge polaritons by defect structures is found to be in good agreement with finite-difference time-domain simulations. Our findings reveal the extraordinary capability of hyperbolic polariton propagation to cope with the presence of defects, providing an excellent basis for applications such as nanooptical circuitry, nanoscale cloaking and nanoscopic quantum technology.

Charting the Exciton–Polariton Landscape of WSe2 Thin Flakes by Cathodoluminescence Spectroscopy

“…Edge polaritons, in contrast to surface polaritons, are spatially confined to and propagate along the pristine edges of the flakes. [11,43] The spatial confinement and different screening mechanism of edge exciton-polaritons compared to bulk excitons lead to lower attenuation constants and shifted exciton energies. By scanning the edge of a WSe 2 flake with a trapezoidal geometry (Figure 4a), spatial interference fringes of up to several orders are observed (Figure 4b), due to lower attenuation constants compared to surface polaritons.…”

“…More specifically, excitons in semiconducting group VI transition-metal dichalcogenides (TMDCs) are advantageous because of their exceptionally high binding energies of a few 100 meV giving rise to stable and robust exciton excitations at room temperature. [10][11][12] In addition, the high oscillator strengths associated with the excitonic resonances result in exciton lifetimes longer than 100 fs, enabling effective light-mater coupling. [13] For these reasons, TMDCs are now a particularly fruitful platform for the observation of strong coupling effects between excitons and photons [14] including the formation of exciton-polariton quasiparticles with effective masses reduced by several orders of magnitude.…”

Topological Materials for Functional Optoelectronic Devices

“…[ 146 ] Dyakonov plasmons and edge polaritons have also been reported in Bi 2 Se 3 nanoplates. [ 147,148 ] In most cases, the plasmonic properties seem to be related mostly with the interband‐induced negative bulk permittivity values () of the considered chalcogenide in the ultraviolet–visible, although in some cases the surface dielectric permittivity was proposed to play a significant role. [ 124 ] The spectral features of the plasmon resonances reported in such nanostructures were shown to be tunable by design.…”

Plasmon–Exciton Interactions in Nanometer-Thick Gold-WSe2 Multilayer Structures: Implications for Photodetectors, Sensors, and Light-Emitting Devices

“…9,10 Among these excitonic materials, the TMDCs with molybdenum(Mo) and tungsten (W) transition metals distinct themselves as high-refractive-index materials, with large exciton binding energies. 11,12 Moreover, a sub-wavelength-thick WSe 2 flake by itself shows intriguingly a strong exciton−photon coupling effect. 10,13,14 Hence, the optical volume mode reduction is one of the critical routes to further enhance and control the light−matter coupling strength.…”