Negative refraction at deep-ultraviolet frequency in monocrystalline graphite

TL;DR

This paper demonstrates negative refraction in natural monocrystalline graphite at deep-ultraviolet frequencies, revealing a new natural negative-index material with potential applications in nanolithography and ultraviolet hyperlenses.

Contribution

It reports the first observation of negative refraction at all incident angles in a natural material, due to strong anisotropy causing indefinite permeability.

Findings

Negative refraction observed at 254 nm in graphite

Negative refraction occurs for incident angles 20° to 70°

Potential for ultraviolet hyperlens development

Abstract

Negative refraction is such a prominent electromagnetic phenomenon that most researchers believe it can only occur in artificially engineered metamaterials. In this article, we report negative refraction for all incident angles for the first time in a naturally existing material. Using ellipsometry measurement of the equifrequency contour in the deep-ultraviolet frequency region (typically 254 nm), obvious negative refraction was demonstrated in monocrystalline graphite for incident angles ranging from 20o to 70o. This negative refraction is attributed to extremely strong anisotropy in the crystal structure of graphite, which gives the crystal indefinite permeability. This result not only explores a new route to identifying natural negative-index materials, but it also holds promise for the development of an ultraviolet hyperlens, which may lead to a breakthrough in nanolithography, the most critical technology necessary for the next generation of electronics.