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

• Published in: Scientific reports Vol. 6; no. 1; p. 27700
• Main Authors: Kaipurath, R. M., Pietrzyk, M., Caspani, L., Roger, T., Clerici, M., Rizza, C., Ciattoni, A., Di Falco, A., Faccio, D.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 13-06-2016; Nature Publishing Group
• Subjects: 639/624/399/1015; 639/624/400/385; Electrons; Humanities and Social Sciences; Measurement techniques; multidisciplinary; Phase transitions; Science; Silver
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/srep27700

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-Near-Zero (ENZ) 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 ENZ wavelength, further supporting an optically induced change in the physical behaviour of the metamaterial.