拓扑材料等离激元谱学研究

Plasmonics plays an important role in the development of nanophotonics, which allows breaking diffraction limit and controlling light in deep-subwavelength scale due to the strong interaction between light and free carriers. Noble metals and 2-dimensional electron gas have been the main platforms for studying plasmonics over the past decade. The metal-based plasmonic devices have exhibited great potential in various applications, including integrated photonic systems, biological sensing, super-resolution imaging and surface-enhanced Raman scattering, etc. Because of the high carrier density, plasmons of noble metals are realized in the near-infrared to visible frequency range. With the rapid development of new materials, many other plasmonic materials are discovered to exhibit new properties. One example is the graphene plasmons working in the mid-infrared and terahertz spectral range, which exhibit strong field confinement and frequency tunability due to the massless Dirac fermions and other exotic electrical and optical properties. Recently, topological materials, the band structures of which are composed of cones with linear dispersion like in graphene, are discovered, such as the topological insulators, Dirac semimetals, Weyl semimetals and nodal line semimetals, providing another platform to study the Dirac plasmons. Such linear dispersion results in small electron mass and unique carrier density dependence of plasmons. In addition, topological materials possess a tremendous amount of exotic electron properties, such as the ultrahigh mobility, topological surface states and chiral anomaly in Weyl semimetals, etc. Many of these electronic properties can be inherited by the collective oscillation of free electrons, promising new possibility for plasmonics. Here, the experimental observations of plasmons in topological insulators and topological semimetals are reviewed, with special focus on the studies based on electron energy loss spectrum and Fourier transform infrared spectroscopy. At the end, other topological materials with potential for hosting 2D plasmons are discussed. This review provides an overview of plasmons in topological semimetals and may stimulate further quest of more exotic features for plasmons.