Optically induced metal-to-dielectric transition in Epsilon-Near-Zero metamaterials

TL;DR

This paper demonstrates an optically induced, reversible transition in epsilon-near-zero metamaterials from metallic to dielectric behavior, driven by ultrafast pump pulses, with potential for dynamic optical control.

Contribution

It introduces a method to control the dielectric properties of epsilon-near-zero metamaterials using ultrafast optical pumping, revealing a linear, non-tuned, and reversible transition.

Findings

Transition from negative to positive permittivity near EEZ wavelength

Linearity of permittivity change with pump power

Transition occurs on ~100 fs timescale

Abstract

Epsilon-Near-Zero materials exhibit a transition in the real part of the dielectric permittivity from positive to negative value as a function of wavelength. Here we study metal-dielectric layered metamaterials in the homogenised regime (each layer has strongly subwavelength thickness) with zero real part of the permittivity in the near-infrared region. By optically pumping the metamaterial we experimentally show that close to the Epsilon-Equal-to-Zero (EEZ) wavelength the permittivity exhibits a marked transition from metallic (negative permittivity) to dielectric (positive permittivity) as a function of the optical power. Remarkably, this transition is linear as a function of pump power and occurs on time scales of the order of the 100 fs pump pulse that need not be tuned to a specific wavelength. The linearity of the permittivity increase allows us to express the response of the metamaterial in terms of a standard third order optical nonlinearity: this shows a clear inversion of the roles of the real and imaginary parts in crossing the EEZ wavelength, further supporting an optically induced change in the physical behaviour of the metamaterial.