拓扑材料等离激元谱学研究

Spectroscopic studies of plasmons in topological materials

等离激元光子学是现代光电子科学重要的组成部分.除了传统的基于贵金属的等离激元研究,随着新材料的快速发展,越来越多具有新颖的等离激元性质的材料被发现.典型的例子是具有高局域性和可调节性的石墨烯等离激元.随着拓扑理论和实验的快速发展,与石墨烯一样具有狄拉克线性色散的拓扑材料的等离激元光谱研究也取得了长足的进步.本文首先介绍拓扑绝缘体和拓扑半金属的等离激元的谱学实验进展,特别是光谱方面的进展.随后对更多的有潜力适合二维等离激元研究的拓扑材料进行了展望.

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 2 D plasmons are discussed.This review provides an overview of plasmons in topological semimetals and may stimulate further quest of more exotic features for plasmons.