Mid- to Far-Infrared Anisotropic Dielectric Function of HfS2 and HfSe2

Ryan A. Kowalski, Joshua Ryan Nolen, Georgios Varnavides, Sebastian Mika Silva, Jack E. Allen, Christopher J. Ciccarino, Dominik M. Juraschek, Stephanie Law, Prineha Narang, Joshua D. Caldwell

Research output: Contribution to journalArticlepeer-review

Abstract

The far-infrared (far-IR) remains a relatively underexplored region of the electromagnetic spectrum extending roughly from 20 to 100 µm in free-space wavelength. Research within this range has been restricted due to a lack of optical materials that can be optimized to reduce losses and increase sensitivity, as well as by the long free-space wavelengths associated with this spectral region. Here the exceptionally broad Reststrahlen bands of two Hf-based transition metal dichalcogenides (TMDs) that can support surface phonon polaritons (SPhPs) within the mid-infrared (mid-IR) into the terahertz (THz) are reported. In this vein, the IR transmission and reflectance spectra of hafnium disulfide (HfS2) and hafnium diselenide (HfSe2) flakes are measured and their corresponding dielectric functions are extracted. These exceptionally broad Reststrahlen bands (HfS2: 165 cm−1; HfSe2: 95 cm−1) dramatically exceed that of the more commonly explored molybdenum- (Mo) and tungsten- (W) based TMDs (≈5–10 cm−1), which results from the over sevenfold increase in the Born effective charge of the Hf-containing compounds. This work therefore identifies a class of materials for nanophotonic and sensing applications in the mid- to far-IR, such as deeply sub-diffractional hyperbolic and polaritonic optical antennas, as is predicted via electromagnetic simulations using the extracted dielectric function.

Original languageEnglish
Article number2200933
JournalAdvanced Optical Materials
Volume10
Issue number23
DOIs
StatePublished - 5 Dec 2022

Keywords

  • dielectric function
  • far-infrared
  • nanophotonics
  • polaritons
  • transition-metal dichalcogenides

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Atomic and Molecular Physics, and Optics

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