Physics and Applications of Epsilon-Near-Zero Materials

Dear colleagues,

Metamaterials have attracted a great deal of research interest in the last twenty years, since their unusual electromagnetic properties have brought to light novel electromagnetic regimes and have suggested a number of ultimate devices for extreme radiation steering.

Materials exhibiting very small dielectric permittivity, or epsilon-near-zero (ENZ) materials, belong to the family of media able to affect electromagnetic radiation in a very unconventional way because the medium effective wavelength is much larger than the vacuum wavelength so that they host a regime where both field amplitude and phase are slowly-varying over relatively large portions of the bulk. Such a key feature allows the electromagnetic field to be manipulated down to its finest details, and it can be put to work to achieve a number of different functionalities. Examples are ”squeezing” electromagnetic waves at will, tailoring the antenna radiation pattern, achieving perfect absorption, enhancing spatial dispersion, and achieving novel cloaking mechanisms.

Other interesting phenomena arise when the ENZ regime is combined with matter nonlinearity since their crucial interplay allows the all-optical transition from dielectric to metal behavior of the medium. Furthermore, such interplay benefits from the nonresonant enhancement of the normal electric field component across the vacuum–ENZ medium interface, producing intriguing effects like transmissivity directional hysteresis and enhancement of second and third harmonic generation.

Even though most of the above intriguing ENZ effects have been predicted and observed in metamaterials, an increasing research interest has recently been focused on plasmonic materials having a zero-crossing point of the permittivity real part close to their plasma frequency. Examples are semiconductors, strontium ruthenate, aluminum-doped zinc oxide, and indium tin oxide. Such plasmonic materials are intrinsically tunable, since their plasma frequency can be varied using electrical or optical methods and, hence, the ENZ frequency and bandwidth can be suitably adjusted for designing novel plasmonic devices with an optical steering functionality.

Dr. Alessandro Ciattoni
Guest Editor

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