ACS Photonics, Just Accepted Manuscript
DOI: 10.1021/ph4000983
Publication Date (Web): February 14, 2014
Copyright © 2014 American Chemical Society
http://pubs.acs.org/doi/abs/10.1021/ph4000983?journalCode=apchd5
A class of strongly anisotropic materials having their principal elements of dielectric permittivity or magnetic permeability tensors of opposite signs, so-called indefinite or hyperbolic materials, has recently attracted a significant attention. These materials enabled such novel properties and potential applications as all-angle negative refraction, high density of states, and imaging beyond diffraction limit using a so-called hyperlens. While several studies identified a few examples of negative refractions in birefringence crystals existing in nature, a majority of optical materials with hyperbolic dispersion relations known to date are engineered composite materials, “metamaterials,” such as metal-dielectric subwavelength multilayered structures or metal nanowires in a dielectric matrix. In this paper, we investigate naturally existing hyperbolic materials with indefinite permittivity for a range of frequencies from terahertz to ultraviolet. These include graphite, MgB2, cuprate and ruthenate. Spectroscopic ellipsometry is used to characterize the dielectric properties of graphite and MgB2, and a fitting method based on reflectance spectra is used to determine the indefinite permittivity of the cuprate and ruthenate. Lastly, we discuss the mechanisms behind indefinite properties of these materials.
