Visualizing Material 'Twist' Like a Map with Terahertz Waves: New Spectroscopic Imaging Technology to Support Next-Generation Materials and Communications

A research team comprising Ms. Uina Chiba (formerly a master's student at the Graduate School of Science and Engineering, Chiba University), Professor Katsuhiko Miyamoto of the Graduate School of Engineering, Chiba University, Assistant Professor Seigo Ohno of the Graduate School of Science, Tohoku University, and Group Leader Takeo Minari of the National Institute for Materials Science (NIMS) has developed a new spectroscopic imaging technology. This technology uses an artificial structure called a 'moiré metasurface' made of stacked silver micro-disks to directly observe the spatial distribution of right- and left-handed chirality in materials as two-dimensional images using terahertz (THz) waves. Conventional terahertz circular dichroism (CD) measurements could only obtain averaged information from the entire sample, making it difficult to capture differences in chirality from one location to another. This study succeeded in visualizing the coexistence of different chiralities for the first time in the world. This achievement is expected to be applied to quality evaluation of next-generation materials, analysis of biomolecular structures, and development of new terahertz devices. The research results were published in the academic journal ACS Photonics on June 2, 2026 (Eastern Time). (Paper: 10.1021/acsphotonics.6c00372)

Figure: Terahertz circular dichroism imaging and spectroscopy results: The reversal of right- and left-handed chirality responses corresponding to the mirror-image relationship of the structure is observed. This demonstrates the ability to visualize the chirality distributed within a material as a two-dimensional image.

■ Research Background

Materials possess a property called 'chirality,' where a mirror image cannot be superimposed on the original, like right-handed and left-handed screws. A representative method for investigating this chirality is 'circular dichroism (CD) measurement,' widely used in drug discovery and materials science. Terahertz waves are particularly sensitive to the 'low-energy' dynamics of materials, such as molecular vibrations and protein higher-order structures, making them a focus for examining three-dimensional 'twist' structures that are difficult to see with visible light or infrared. However, conventional terahertz CD measurements were predominantly 'point measurements' that averaged the entire sample. This posed a challenge: if different chiralities were distributed within the sample, their signals would cancel each other out, preventing the acquisition of local structural information. Against this background, there was a strong need for a new measurement technology that could directly 'visualize' the spatial distribution of chirality.

■ Key Research Results

1. Development of the world's first high-precision terahertz chirality imaging technology: A spectroscopic imaging device was constructed that can accurately distinguish between 'right-handed' and 'left-handed' light over a very wide frequency band of 3 to 6 terahertz. This enables mapping of chirality distribution with a spatial resolution on the order of the thickness of a human hair.

2. Freely designing twists using the artificial 'moiré' structure: The team utilized the 'moiré pattern' generated by stacking sheets of silver disks with a slight angular offset. This artificial structure (metasurface) was used to artificially create a state where right- and left-handed chiralities are complexly mixed, serving as a verification model.

3. Direct observation of 'right-twist' and 'left-twist' reversal phenomena: Imaging results visualized the alternating arrangement of 'regions exhibiting right-handed properties' and 'regions exhibiting left-handed properties' within a single sheet. This is a phenomenon that could never be observed with conventional averaged measurements.

4. Elucidation of the interaction mechanism between micro- and macro-structures: The team proved both theoretically and experimentally that both the arrangement of individual disks (microstructure) and the large pattern generated by stacking (macrostructure) govern the interaction with terahertz waves.

■ Future Outlook

The imaging platform established in this study is expected to be extended to a wider frequency band of 2 to 15 terahertz in the future. The 'visualization of twists' using terahertz waves is anticipated to be applied as a new foundational technology for analyzing invisible microstructures in the following fields:

Medical/Drug Discovery: New diagnostic technology for visualizing the distribution of abnormal protein aggregates (e.g., amyloid).

Ultra-Fast Communications: Evaluation and inspection of advanced signal control devices that utilize light's twist, required for next-generation communications (6G).

New Materials Development: Detection of fine structural distortions inside quantum materials and soft materials, leading to analytical techniques for improving material properties.

■ Glossary

Note 1) Moiré Metasurface: A planar material that artificially realizes a moiré structure for terahertz waves by stacking two regular microstructures with a slight offset. This enables unique wave control through 'twist structures' that do not normally appear.

Note 2) Chirality: The property of an object or molecule where its mirror image cannot be superimposed on the original. The relationship between a right-handed and left-handed screw is a typical example. The difference in 'right' or 'left' orientation significantly affects the properties and functions of materials. Distinguishing this difference is crucial in drug discovery and materials science.

Note 3) Terahertz (THz) Waves: Electromagnetic waves located between radio waves and light (infrared), with a frequency band oscillating about one trillion times per second. They are sensitive to collective vibrations and soft motions of molecules and materials, attracting attention as a means to investigate the internal structure of materials invisible to visible light.

Note 4) Circular Dichroism (CD): The property of a material showing different responses to right- and left-handed circularly polarized light. It is a representative method for investigating the 'right- or left-handed twist' of materials and is widely used in analyzing the three-dimensional structure of molecules and materials.

■ Paper Information

Title: Multiscale chirality in moiré metasurfaces revealed by terahertz circular dichroism spectroscopic imaging

Authors: Uina Chiba, Shota Tsuji, Gaku Oritani, Takumi Yoichi, Rinpei Sasaki, Takeo Minari, Seigo Ohno, Katsuhiko Miyamoto

Journal: ACS Photonics

DOI: 10.1021/acsphotonics.6c00372

■ About the Research Project

This research was supported by the following grants:

・Grants-in-Aid for Scientific Research (JP23K23248, JP24KK0108, JP22K18979, JP23K04567) from the Japan Society for the Promotion of Science (JSPS)

・FOREST Program (JPMJFR2036) from the Japan Science and Technology Agency (JST), among others.