With advances in nanofabrication techniques, extreme-scale nanophotonic devices with critical gap dimensions of just 1–2 nm have been realized. Plasmons in such ultranarrow gaps can exhibit nonlocal response, which was previously shown to limit the field enhancement and cause optical properties to deviate from the local description. Using atomic layer lithography, we create mid-infrared-resonant coaxial apertures with gap sizes as small as 1 nm and observe strong evidence of nonlocality, including spectral shifts and boosted transmittance of the cutoff epsilon-near-zero mode. Experiments are supported by full-wave 3-D nonlocal simulations performed with the hybridizable discontinuous Galerkin method. This numerical method captures atomic-scale variations of the electromagnetic fields while efficiently handling extreme-scale size mismatch. Combining atomic-layer-based fabrication techniques with fast and accurate numerical simulations provides practical routes to design and fabricate highly-efficient large-area mid-infrared sensors, antennas, and metasurfaces.
Bibliographical noteFunding Information:
The authors thank Prof. John Pendry, Prof. Javier Aizpurua, and Prof. Luis Martin-Moreno for helpful discussions and comments. D.Y. and S.-H.O. acknowledge support from the U.S. National Science Foundation (ECCS 1610333 and ECCS 1809240). F.V.-C., N.-C.N., and J.P. acknowledge support from the Air Force Office of Scientific Research (AFOSR) Grant No. FA9550-15-1-0276 and FA9550-16-0214. C.C. acknowledges support from AFOSR No. FA9550-17-1-0177. D.R.S. acknowledges funding from AFOSR (Grant No. FA9550-18-1-0187). C.C. and S.-H.O. also acknowledge partial support from the Institute of Mathematics and its Applications (IMA) at the University of Minnesota. S.-H.O. further acknowledges support from the Sanford P. Bordeau Endowed Chair in Electrical Engineering at the University of Minnesota and the McKnight Foundation.