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: England Nature Publishing Group 13.06.2016
• Subjects: Electrons; Measurement techniques; Phase transitions; 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.