This strange crystal acts like metal and glass at the same time

Amazing stuff!

"A remarkable crystal called molybdenum oxychloride could help make futuristic technologies like smart contact lenses and ultrathin AR [augmented reality] glasses a reality. Scientists have created the first detailed experimental map of its optical properties, revealing the strongest light-bending effect ever measured in a natural material. The crystal can act either like a reflective metal or transparent glass, allowing it to manipulate light with extraordinary efficiency while being thousands of times thinner than a human hair. ...

When positioned one way, it reflects light much like a metal. Rotate it by 90 degrees, and it becomes transparent like glass. This unusual characteristic stems from its extreme optical anisotropy, meaning its properties vary dramatically depending on direction. ...

Rare Light-Slowing Effect Found in Visible Light

The researchers also identified a rare epsilon-near-zero point at 512 nm (green light).

At this point, part of the material's optical response falls almost to zero. As a result, light effectively slows down while the electric field inside the crystal becomes stronger. This combination can significantly enhance interactions between light and matter. ..."

From the abstract:

"The realization of extreme optical anisotropy is foundational for nanoscale light manipulation.

The van der Waals (vdW) crystal MoOCl2 has emerged as a promising candidate for this quest, hosting hyperbolic plasmon polaritons in the visible and near-infrared wavelengths. However, the fundamental anisotropic dielectric tensor governing this behavior has remained elusive.

Here, we resolve this problem by providing the first experimental determination of the full dielectric tensor of hyperbolic vdW MoOCl2. Via spectroscopic ellipsometry, Mueller matrix, and reflectance measurements, we quantify the material’s optical duality: a metallic optical response (ε1 < 0) along the crystallographic a-axis and a dielectric response (ε1 > 0) along the orthogonal directions.

This dichotomy drives an epsilon-near-zero (ENZ) condition at ≈512 nm and results in a giant in-plane birefringence of Δn ≈ 2.2 for MoOCl2. As a result, our work provides the critical missing experimental parameters for MoOCl2, establishing it as a benchmark hyperbolic and ENZ material."

This strange crystal acts like metal and glass at the same time | ScienceDaily "A newly mapped crystal can manipulate light in astonishing ways, opening the door to ultrathin AR glasses, smart contact lenses, and tiny high-speed optical chips."

Giant Optical Anisotropy and Visible-Frequency Epsilon-near-Zero in Hyperbolic van der Waals MoOCl2 (open access)

Credits: Neuer Kristall macht optische Bauteile tausendfach dünner

Graphical abstract