# Layered superconductors as negative-refractive-index metamaterials

## TL;DR

This paper explores layered superconductors as potential negative-refractive-index metamaterials, analyzing their properties and limitations for use in advanced optical applications.

## Contribution

It provides a detailed analysis of layered superconductors' electromagnetic properties, highlighting challenges in achieving low-loss negative refraction.

## Key findings

- Low-Tc superconductors can achieve negative refraction with low losses.
- High-Tc superconductors exhibit large in-plane conductivity, leading to significant losses.
- Enhancing evanescent modes in layered superconductors remains challenging.

## Abstract

We analyze the use of layered superconductors as anisotropic metamaterials. Layered superconductors can have a negative refraction index in a wide frequency range for arbitrary incident angles. Indeed, low-Tc (s-wave) superconductors allow to produce artificial heterostructures with low losses for T<<Tc. However, the real part of their in-plane effective permittivity is very large. Moreover, even at low temperatures, layered high-Tc superconductors have a large in-plane normal conductivity, producing large losses (due to d-wave symmetry). Therefore, it is difficult to enhance the evanescent modes in either low-Tc or high-Tc superconductors.