Infrared plasmons propagate through a hyperbolic nodal metal

Abstract

Metals are canonical plasmonic media at infrared and optical wavelengths, allowing one to guide and manipulate light at the nanoscale. A special form of optical waveguiding is afforded by highly anisotropic crystals revealing the opposite signs of the dielectric functions along orthogonal directions. These media are classified as hyperbolic and include crystalline insulators, semiconductors, and artificial metamaterials. Layered anisotropic metals are also anticipated to support hyperbolic waveguiding. However, this behavior remains elusive, primarily because interband losses arrest the propagation of infrared modes. Here, we report on the observation of propagating hyperbolic waves in a prototypical layered nodal-line semimetal ZrSiSe. The observed waveguiding originates from polaritonic hybridization between near-infrared light and nodal-line plasmons. Unique nodal electronic structures simultaneously suppress interband loss and boost the plasmonic response, ultimately enabling the propagation of infrared modes through the bulk of the crystal.

Topological Insulator Metamaterials

“…Theory has predicted that the collective dynamics of electrons on both the open-segment and closed Fermi surfaces in Weyl semimetals with broken time reversal symmetry leads to the creation of Fermi arc plasmons with hyperbolic dispersion and chiral nature, that could allow for tight focusing of collimated, nonreciprocal surface plasmon waves with frequency-dependent directionality . Such hyperbolic plasmons have been demonstrated in WTe 2 and ZrSiSe very recently. , Furthermore, Weyl semimetals in the presence of a magnetic field are predicted to support two types of highly confined 3D topological plasmons with anisotropic dispersions, from linear to parabolic or even hyperbolic bands . Hybridizing such materials with suitable metamaterial structures could provide additional degrees of freedom to control and enhance light–matter interaction.…”

“…142 Recently, 3D hyperbolic plasmons in layered nodalline semimetal ZrSiSe was demonstrated in the telecom band via near-field microscopy measurements. 143 Topological semimetals are also suitable candidates to generate highly chiral photocurrents. Very promising preliminary studies were conducted by Ma et al, who detected chirality of the Weyl fermions through the photocurrent generated in TaAs crystals by circularly polarized mid-infrared light illumination, 144 and by Ji et al, who investigated the spatially dispersive nature of the circular photogalvanic effect in Mo x W 1−x Te 2 semimetal.…”

“…136 Such hyperbolic plasmons have been demonstrated in WTe 2 and ZrSiSe very recently. 142,143 Furthermore, Weyl semimetals in the presence of a magnetic field are predicted to support two types of highly confined 3D topological plasmons with anisotropic dispersions, from linear to parabolic or even hyperbolic bands. 138 Hybridizing such materials with suitable metamaterial structures could provide additional degrees of freedom to control and enhance light− matter interaction.…”

“…Low-energy optical transition related to the Weyl point/anticrossing line has been suggested to be the main mechanism behind the giant magneto-optical transitions. , Natural hyperbolic optical properties of a candidate Weyl semimetal WeTe 2 enabled to realize far-infrared 2D hyperbolic plasmons in the range between 16 and 23 μm . Recently, 3D hyperbolic plasmons in layered nodal-line semimetal ZrSiSe was demonstrated in the telecom band via near-field microscopy measurements . Topological semimetals are also suitable candidates to generate highly chiral photocurrents.…”

Hyperbolic polaritons in topological nodal ring semimetals

“…Note that in "conventional" Weyl semimetals with nodal points the hyperbolic dispersion was only predicted in high magnetic fields and with Fermi level tuned to the band crossing points [11]. Note also that in a relatively better studied group of open nodal line semimetals the hyperbolic dispersion has been recently observed with tip-enhanced infrared spectroscopy [30].…”