Hyperbolic metamaterials with extreme mechanical hardness

TL;DR

This paper introduces a new class of hyperbolic metamaterials that combine extreme mechanical hardness with hyperbolic optical properties, identified through high-throughput calculations and experimental validation, expanding potential applications in harsh environments.

Contribution

It demonstrates the design and validation of hyperbolic metamaterials with tunable mechanical properties, including extreme hardness, using first-principles calculations and effective medium theory.

Findings

Identified hard and ultrasoft hyperbolic metamaterials among 1800+ combinations.

Validated the mechanical and optical properties experimentally.

Expanded the potential for optical applications in harsh environments.

Abstract

Hyperbolic metamaterials (HMMs) are highly anisotropic optical materials that behave as metals or as dielectrics depending on the direction of propagation of light. They are becoming essential for a plethora of applications, ranging from aerospace to automotive, from wireless to medical and IoT. These applications often work in harsh environments or may sustain remarkable external stresses. This calls for materials that show enhanced optical properties as well as tailorable mechanical properties. Depending on their specific use, both hard and ultrasoft materials could be required, although the combination with optical hyperbolic response is rarely addressed. Here, we demonstrate the possibility to combine optical hyperbolicity and tunable mechanical properties in the same (meta)material, focusing on the case of extreme mechanical hardness. Using high-throughput calculations from first principles and effective medium theory, we explored a large class of layered materials with hyperbolic optical activity in the near-IR and visible range, and we identified a reduced number of ultrasoft and hard HMMs among more than 1800 combinations of transition metal rocksalt crystals. Once validated by the experiments, this new class of metamaterials may foster previously unexplored optical/mechanical applications.