by the geometry rather than the constituent materials, which led to the field of metamaterials. Over the last decades, metamaterials research has grown exponentially due to the exceptional possibilities that they offer to manipulate light. Examples of extraordinary properties include artificial chirality, [1] super absorption, [2] extraordinary optical transmission, [3] optical magnetism, [4] or negative refraction. [5] From the several reported structures for achieving negative index metamaterials (NIMs) at optical frequencies, the multilayer fishnet design stands out as the most promising architecture in terms of tunability, figure of merit (FOM), and strong negative values. [6] Its design lies on metal-insulator-metal (MIM) stacks drilled with a 2D periodic array of holes. When the metallic layers are close enough, the propagating surface plasmon polaritons (SPPs) at the internal interfaces overlap, leading to the excitation of so-called gap surface plasmons (GSPs). [7] In this situation, out-of-phase currents are generated in the metallic strips, inducing a magnetic dipole in the insulator layer. This artificial magnetism along with the electric response arising from the metallic layers are the source of the negative refractive index (RI). [8] In the recent years, there has been an increasing interest in the commercial applications of metamaterials. However, the implementation of these architectures in an actual device is not an easy task. Recent advances in nanofabrication have enabled the high-throughput and up scalable production of NIMs using patterning methods such as self-assembly [9-11] or nanoimprint lithography (NIL), [12,13] where the proper arrangement gave rise to negative index at optical frequencies. In particular, the inspiring works by Gao et al. [13] demonstrated large area metamaterials operating at visible and telecommunication frequencies using a subtractive lift-off process combined with metal evaporation and reactive ion etching. Despite the scalability of the patterning techniques used in these works, most of them involve several steps, make use of top-down expensive methods such as electron beam evaporation or implies transferring steps that can damage the structures. In terms of the absolute values achieved, there is still room for improvement for large area NIMs. A record value of −0.73 at 710 nm being the lowest negative refractive index achieved in the visible range with an scalable technique so far. [13] It is also worth noting that obtaining NIMs with a negligible angular Negative index metamaterials have revolutionized the field of photonics because of their unconventional electromagnetic properties absent in naturally occurring materials. It remains a challenge however, to achieve strong negative refractive index at optical frequencies over large areas in a device compatible fashion. In this work, a scalable method for the straightforward production of fishnet-like negative index metamaterials combining soft nanoimprinting and electrodeposition is reported. In four simple steps...

No abstract