Team led by Prof. Seungwoo Lee achieves world’s highest refractive index

Study on refractive index exceeding natural upper limit published in Nano Letters

▲ Graduate student Ji-Hyeok Huh (first author), graduate student Jaewon Lee (co-author), 

Professor Seungwoo Lee (corresponding author)

The research team led by Professor Seungwoo Lee of the KU-KIST Graduate School of Converging Science and Technology at Korea University achieved the world’s highest refractive index in optical frequency based on self-assembly.

The results were published in the international journal Nano Letters on April 2.

-Author information: Ji-Hyeok Huh (first author, Korea University), Jaewon Lee (co-author, Korea University), Professor Seungwoo Lee (corresponding author, Korea University)

-Title of paper: Soft Plasmonic Assemblies Exhibiting Unnaturally High Refractive Index

-Journal of publication: Nano Letters (Published online on April 2, 2020, https://pubs.acs.org/doi/10.1021/acs.nanolett.0c00422)

The refractive index of a material is a basic value that determines various optical properties. This value is limited by the upper limit of the electrical dipole moment, which can be induced depending on charge density and conductivity. The team designed meta-atoms based on naturally occurring atoms, and crystallized them through self-assembly to achieve ultra-high-refractive indices in optical regimes, including near-infrared and mid-infrared.

In particular, the team produced metamaterials through the self-assembly and crystallization of metallic nanocube particles at a fluidic interface. The electric dipole moment in meta-atoms within the self-assembled metamaterials amplified to unnatural levels due to the accumulation of charges. The resulting refractive index was as high as 6.4, which exceeds the natural upper limit of 4.0. This is the highest refractive index in optical regimes reported to date.

▲ Metamaterials having unnaturally high refractive indices.

Metallic nanocubes serving as meta-atoms in optical regimes can amplify electric dipole moment when crystallized through self-assembly, thus exceeding naturally available refractive indices.