Authors
Urvi Parekh, Achyut Tiwari, Bruno Gompf, Nadiia Didukh, Jivesh Kaushal, Stefan Scheel, Christian Klinke, Rostyslav Lesyuk
Published in
Nano letters. Oct 12, 2026. Epub Oct 12, 2026.
Abstract
Hyperbolic media support high-k electromagnetic modes, enabling subdiffractional confinement, anomalous refraction, and enhanced light-matter interactions. While most hyperbolic metamaterials rely on artificial structuring, natural hyperbolicity arises from crystal anisotropy and direction-dependent plasma frequencies. Here we provide direct experimental evidence for natural hyperbolicity in copper chalcogenides by spectroscopic ellipsometry in the visible-near-infrared range. We demonstrate hyperbolic dispersion in bulk covellite CuS by identifying a spectral window where the real parts of the in-plane and out-of-plane permittivity components have opposite signs. The study is then expanded to size-controlled CuS nanosheets as oriented films. Using the Bruggeman effective medium approximation to account for the nanostructure/void composite, we show that hyperbolicity persists upon nanoscaling and that the epsilon-near-zero condition and hyperbolic bandwidth shift with size. Finally, we demonstrate analogous behavior in klockmannite CuSe nanosheets, establishing copper chalcogenides as a tunable platform for natural hyperbolicity at the boundary of the NIR and visible ranges.
PMID:
42863087
Bibliographic data and abstract were imported from PubMed on 13 Oct 2026.
Read full publication at:
Please sign in
to see all details.
Advertisement
Stats
- Recommendations n/a n/a positive of 0 vote(s)
- Views 5
- Comments 0