Smolyaninova and Smolyaninov argue that the ε-near-zero (ENZ) approach to designing metamaterials could offer a blueprint for creating a material with the appropriate value of ε. ENZ metamaterials are mixtures of metallic and dielectric components and in their proposal the metal is also a conventional superconductor – these are metals such as lead and mercury that have Tc values below 10 K.
The ENZ metamaterial proposed by the researchers involves making a superconductor with random “inclusions” of dielectric material. Smolyaninova told physicsworld.com that a possible candidate for the dielectric is the ferroelectric material strontium titanate, which can be made in nanoparticle form. The sizes of the inclusions and typical distances between them must be smaller than the correlation length between electron pairs in the superconductor – which is about 100 nm.
Another design proposed by the team is a “hyperbolic” metamaterial in which the desired ε is engineered using alternating layers of metallic and dielectric materials. Indeed, the researchers point out that typical high-Tc superconductors do share some properties with hyperbolic metamaterials. Again, the metal would be a conventional superconductor.
“We are working on actual metamaterial designs and preparing actual experiments now,” Smolyaninova said. She adds that the ENZ design would be easier to implement than the hyperbolic metamaterial.
Smolyaninova is hopeful that metamaterial superconductors could be made with Tc values above the boiling temperature of liquid nitrogen (77 K). This would make them appropriate for use in systems that currently use high-Tc superconductors.