Chiral plasmonic nanostructures have facilitated a promising method for manipulating the polarization state of light. While a precise structural modification at the nanometer-scale-level could offer chiroptic responses at various wavelength ranges, a system that allows fast response control of a given structure has been required. In this study, we constructed uniformly arranged chiral gold helicoids with cobalt thin-film deposition that exhibited a strong chiroptic response with magnetic controllability. Tunable circular dichroism (CD) values from 0.9°to 1.5°at 550 nm wavelength were achieved by reversing the magnetic field direction. In addition, a magnetic circular dichroism (MCD) study revealed that the gap structure and size-related surface plasmon resonance induced MCD peaks. We demonstrated the transmitted color modulation, where the color dynamically changed from green-tored, by controlling the field strength and polarizer axis. We believe current work broadens our understanding of magnetoplasmonic nanostructure and expands its potential applicability in optoelectronics or optical-communications.

Identifying the three-dimensional (3D) crystal plane and strain-field distributions of nanocrystals is essential for optical, catalytic, and electronic applications. However, it remains a challenge to image concave surfaces of nanoparticles. Here, we develop a methodology for visualizing the 3D information of chiral gold nanoparticles ≈ 200 nm in size with concave gap structures by Bragg coherent X-ray diffraction imaging. The distribution of the high-Miller-index planes constituting the concave chiral gap is precisely determined. The highly strained region adjacent to the chiral gaps is resolved, which was correlated to the 432-symmetric morphology of the nanoparticles and its corresponding plasmonic properties are numerically predicted from the atomically defined structures. This approach can serve as a comprehensive characterization platform for visualizing the 3D crystallographic and strain distributions of nanoparticles with a few hundred nanometers, especially for applications where structural complexity and local heterogeneity are major determinants, as exemplified in plasmonics.

Chiral plasmonics has been actively pursued since pushing its light‐matter interaction to an unnaturally extreme regime. Recently, chirality‐encoded metal–insulator–metal (MIM) motifs have promised compelling advantages in advancing chiroptic responses, as they enable a capacitive coupling and its resultant strong electric and magnetic resonances. However, the deterministic control over chiral MIM working at the visible regime is out of reach. Here, large‐area MIM resonators are demonstrated using non‐lithographically assembled chiral gold nanoparticles (helicoids) and subsequent gold layer deposition, and their boosted chiroptical responses at the visible regime are proven. The thickness of the topcoat Au and the dielectric gap can precisely tune the strength of capacitive coupling. The numerical analyses support that the optimally tuned capacitive coupling in the chiral MIM structure not only strengthens both electric and magnetic dipolar resonances but also makes their spectral positions closer to each other.

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